Instruments of Murder Catching History's Criminals: The Forensics Story

In the act of murder, there is a weapon...

..a crime scene...

..and a body.

All vital evidence in the hunt for the killer.

It's a game of cat and mouse between police and murderer

that used to favour the criminal.

But then something happened that swung the odds in favour of justice.

The arrival of forensic science.

I'm Gabriel Weston.

As a surgeon and writer,

I'm fascinated by the work of the forensic scientist

and the murders they've helped to solve.

In this series...

..I'll explore the cases

that transformed criminal investigation.

Through poison and acid...

..fingerprints and blood.

From the earliest days

to the cutting edge of modern forensics.

In this episode I'll be looking at weapons.

I'll reveal how fundamental the instrument of murder is

for catching the criminal and solving the crime.

There will always be those

who believe they can commit the perfect murder,

who think they can wield a weapon

but conceal their crime.

This is the story of how forensic science has emerged to thwart them,

using the murder weapon to catch the killer.

The year is 1235.

In a remote part of China, a body is discovered in a field.

The victim has been hacked to death.

Distinctive cuts point to a sickle as the murder weapon.

An investigator called Sung Tzu has the job of finding the killer,

and he orders everyone in the village who owns a sickle

to lay it out in the open air.

At first there's nothing to see.

But then a fly lands on one of the blades.

It's soon joined by another, and then, another.

Attracted by invisible traces of blood,

the flies reveal the murder weapon,

and confronted with the evidence, the owner confesses.

It's the earliest written account we have

of forensic science being used to identify the murder weapon

and, hence, the killer.

Forensics has elevated the murder weapon

from its role as mere evidence

to that of key witness.

But the story of this progress is a dark one,

complete with hatred, passion, blood and gore.

And it starts at a time when the most popular weapon

was routinely being used without being discovered.

A weapon that left no trace.

Southwest France, 1840.

24-year-old Marie Lafarge

is preparing eggnog for her new husband,

who has suddenly fallen ill.

As Marie adds some white powder,

family friend Anna Brun grows suspicious.

Marie claims she's simply adding sugar,

but Anna doesn't believe her.

She suspects it's poison,

but she has no way to prove it.

Marie had been married for just five months.

She had grown up in affluent Parisian society

but, when her parents died, she was left with little money.

When, at the ripe old age of 23,

she was still unmarried,

Marie's relatives took matters into their own hands.

Marie's uncle consulted a marriage broker

and he selected an eligible bachelor for her,

a wealthy businessman called Charles Lafarge.

Now, it's clear that Marie didn't find him at all prepossessing,

in fact, in her diary she called him exceedingly ugly.

But she wasn't marrying for love - it was a business deal,

and she accepted his proposal.

The day after their wedding,

the couple travelled south together to Charles' large estate.

When Marie arrived at her new home she realised she'd been conned.

She'd been expecting a grand estate with lots of servants.

What she found instead was a dilapidated house, full of rats.

Her new husband didn't have any money -

in fact, he was in serious debt.

Distraught, Marie locked herself in a room

and wrote him an impassioned letter,

begging him to release her from the marriage.

But Charles refused.

Marie was trapped.

In December of 1839,

Charles travelled to Paris on business.

Whilst there, he received a surprise parcel from Marie.

A cake, accompanied by a love letter.

Soon after eating the cake, Charles fell violently ill.

He returned home with sickness and a high fever.

Marie undertook to nurse her husband back to health.

She even prepared his food.

But, despite her solicitous attentions, his condition got worse.

Even the family doctor was at a loss,

prescribing eggnog in the hope that all that fat and protein

might build Charles up a bit.

Marie did what the doctor ordered.

And it was while she was making the eggnog

that Anna Brun saw Marie add the white powder.

Anna didn't believe that the powder was sugar, as Marie claimed,

so she hid what was left of the eggnog in a cupboard.

Just two days later, Charles died.

The nature of his death didn't worry the family doctor,

but Anna was troubled by what she'd seen.

She confided in Charles' family and they alerted the police.

Marie was arrested on suspicion of murder.

But suspicion was all it could be,

because there was no evidence that she'd poisoned her husband.

Nothing to suggest that any crime had been committed.

In those days, poison was the weapon of choice.

And one poison above all.

Arsenic.

Arsenic was sold at most hardware stores as a way to control rats.

It was an odourless powder

that caused symptoms common to many natural diseases.

Arsenic was a popular weapon,

precisely because it was impossible to detect.

You might have suspicions that someone had been poisoned,

but there was no way of proving it.

But all that was about to change.

In 1836, four years before Marie was arrested,

a Scottish chemist called James Marsh

had invented a test to detect the presence of arsenic.

The lawyers prosecuting Marie had heard of the Marsh test

and wanted to use it to prove she'd poisoned Charles.

They asked the judge if a toxicologist could be summoned

to test the leftover eggnog

and samples of Charles' organs.

The judge agreed

and called for the world's leading toxicologist

to be brought before the court.

His name was Mathieu Orfila.

In front of a crowded courtroom,

he set to work on Charles' organs.

Here at University College London,

Professor Andrea Sella is going to recreate what he did

So, Andrea, can you show me what the Marsh test consists of

and how to do it?

Well, the Marsh test is a really beautiful chemical test.

We're going to take some zinc

and put it into our flask here.

And the second step is simply going to be

to pour some sulphuric acid.

-You can see down at the bottom...

-You can see the bubbles coming up.

..that there are bubbles beginning to come up.

So, what do we do next, Andrea?

Now things get dangerous,

and that means that we can't have it out here in the open.

'Next, we add our sample.

'A piece of lamb's liver, sprinkled with arsenic.'

And so I'll take the stopper off a tiny bit

and then if you just drop it in there.

If the test works,

the arsenic will react

to produce a highly toxic gas called arsine.

I think we've waited long enough -

this is fizzing quite intensely.

To test for the presence of arsine

and, hence, arsenic,

all you need is a piece of porcelain.

What I'd like you to do is to reach into the fume hood

and very carefully put the dish just above the flame.

If arsine is present,

a black mark will appear on the porcelain.

Just close enough, right into the glow.

And there is the spot.

Look at that.

As the arsine burns, then the arsine is converted back to arsenic metal

and you get that black spot.

So that is a perfectly positive Marsh test.

And so this is a completely positive Marsh test.

'Back in 1840,

'when Orfila held the porcelain up to the flame,

'the courtroom was packed with spectators.'

That audience would have been waiting with bated breath

to find out if this woman,

who claimed that she was innocent, had indeed poisoned her husband.

This is really chemistry as a spectator sport.

And in this case,

there's something really kind of voyeuristic and salacious about it,

because what you know is that, you know,

in a sense the life of someone hangs on this... This one test.

And in front of the expectant crowd,

the cause of Charles Lafarge's death slowly emerged

on a piece of white porcelain.

There was no longer any doubt.

He'd been poisoned.

Marie was found guilty and sentenced to life imprisonment.

In the autobiography she wrote in prison,

she continued to protest her innocence,

saying that Charles had been poisoned by his family,

the arsenic put in his eggnog to frame her.

Public opinion was certainly divided at the time,

but while the identity of the murderer

might have been endlessly contested,

that of the murder weapon itself was not.

Charles had been poisoned by arsenic.

The Marsh test had proved it.

Today, forensic chemistry can reveal far more

than the mere presence of a poison.

It can scrutinise the very atoms of the human body

and reveal truths that a criminal may want to hide.

At the forefront of exciting new research

is Doctor Stuart Black from the University of Reading.

A few weeks ago, I sent off a few strands of my hair to Stuart,

and now I'm here to find out what, if anything,

my hair reveals about me.

So, Stuart, what did you find in my hair?

OK, well, what we've analysed here

is the different elements in your hair,

just everyday elements on the periodic table.

Some are quite rare, in cases,

but some are not there in large abundance.

Things like strontium, lead,

these are elements that occur naturally in food, in water,

in the dust that we're breathing in -

and these accumulate in our hair as we ingest them.

Surprisingly, we all have traces

of metals like strontium and lead in our hair.

And there's something about these elements

that can reveal unique details about us as individuals.

It all hinges on the fact they have atoms with different weights -

known as isotopes.

So if we take lead, for example, it has lots of different isotopes.

There's a lead called 208 lead, 207 lead and 206 lead.

Now, in forensics,

the important thing is that different isotopes

occur in different places.

This means that isotopes in someone's hair

can reveal where they've been.

Recently, I travelled to Australia.

So now I want to know whether Stuart has been able to work that out

just from analysing strands of my hair.

So if we look at the map of strontium isotopes on the globe,

we're looking for values

somewhere in this sort of purpley, dark-blue area.

Now, that focuses on parts of Canada and the US,

very, very northern parts of Scandinavia,

Asia, Australia, and parts of Africa as well.

And if you were conducting this from a forensic point of view,

is there any other way

that you could sort of locate me more specifically than that?

Yeah, the way to improve that sort of precision on the data

is to then look at another isotope ratio,

and the lead isotope ratios for your hair samples

are these yellowy dots.

This the part where you hadn't particularly travelled very far,

and that plots it nicely in the European field.

And then these other two areas up here

plot quite close into this area

which overlaps with the UK and Australia.

And, of course, Australia was one of the areas

in which the strontium sort of...

It certainly was.

So my bet would be you've been to Australia.

I have. I have.

That is amazing, that you've managed to quite correctly locate me.

We were there for three weeks over Christmas, so, my goodness.

So the criminal needs to watch out, don't they?

Now, where in Australia is a bit of a difficult question.

Do you want to hazard a guess, Stuart?

Well, the ones that are closest

are perhaps southern and parts of southeast Australia,

those are the closest areas.

Bang on. Absolutely bang on.

So, I was on the Mornington Peninsula.

So, look at that - absolutely fantastic.

That's good.

Isotope analysis can reveal suspects' recent movements,

which they may be trying to hide.

It can destroy alibis

and expose lies.

It's amazing to think that a criminal can now be betrayed

by the very hair on their head.

Forensic chemistry has come a long way

since the Marsh test was used to convict Marie Lafarge.

Today, toxicology is a routine part

of every murder case.

But when it was first developed back in the 19th century,

it completely changed the way that deaths were investigated.

What might initially be thought of as a natural death

could be revealed as a murder with one simple scientific test.

Poison was no longer easy to disguise.

Forensics could expose it as the murder weapon.

By the start of the 20th century,

poison had fallen out of fashion.

A new kind of weapon was becoming popular.

It killed quickly,

could be easily concealed,

and could be used at a distance.

The gun.

Guns had been expensive.

It was only the shooting and hunting classes who could afford them.

But when men returned from the First World War,

their firearms often came home with them.

Guns weren't just an easy way of killing,

they had another distinct advantage -

they were anonymous.

Detectives turning up at a crime scene

might be able to tell that a gun had been used,

but there was no way of working out which gun was the murder weapon.

But one high-profile murder case

would strip guns of their anonymity forever.

On the 20th of January 1928,

police arrested petty criminal Frederick Browne

on suspicion of robbery.

But when the police searched his property,

they found something unexpected.

A kind of revolver called a Webley.

They were astonished.

For four months they'd been searching all over the country

for a Webley revolver

in connection with the violent murder of one of their colleagues.

And now one had turned up right under their noses.

But was it the murder weapon?

The crime had taken place four months earlier,

near the village of Stapleford Abbotts in rural Essex.

The local constable, PC Gutteridge,

was walking home after his night shift

when he heard a car approaching.

A car driving along a remote country lane

in the early hours of the morning was unusual in the 1920s.

Unusual enough for PC Gutteridge to flag it down.

It would be the last thing he ever did.

About 6am the next morning,

the local postman discovered PC Gutteridge

lying by the side of the road.

He'd been shot four times -

two bullets to the left side of the face,

one in each eye.

Now, there's something about this murder

that feels particularly horrible,

but there was a superstition at the time

that the last thing a person sees

gets imprinted on their retinas.

The killer was trying to avoid being identified.

At 7:45am, Detective Inspector Crockford arrived

and examined the murder scene.

It was clear that PC Gutteridge had been about to take notes

when he was shot.

Crockford suspected he'd flagged down a car.

And before long,

he discovered that a car had been stolen earlier that night

from a house just ten miles away from the murder scene.

It was found the following morning, abandoned.

There were traces of blood on the bodywork.

And its mudguard had been damaged.

Discarded on the floor was a gun cartridge.

Detectives were convinced it had come from the murder weapon,

so could the cartridge lead them to the gun?

The police sent the cartridge

to the one man who might be able to help them -

Robert Churchill, the foremost expert

in the up-and-coming science of ballistics.

Churchill recognised the cartridge

as coming from a Webley revolver,

but that didn't get them much further -

the Webley was a very common weapon in the 1920s.

He examined the cartridge under the microscope,

looking for anything that could narrow down the search.

He discovered a curious mark,

a tiny imperfection shaped like a jockey's cap.

Anyone else might have overlooked it,

but Churchill knew instantly it was an important clue.

Four months later, when the police discovered the Webley revolver

in Robert Browne's possession,

Churchill knew this could be the breakthrough he'd been waiting for.

If he could establish a match between this gun and the cartridge,

he'd have found the murder weapon.

And to discover what he did next,

I've come to the National Ballistics Intelligence Service

to meet forensic ballistics expert Martin Parker.

The first step is to fire the gun,

and Martin has an original Webley.

It will be a new experience for me.

I've never fired a gun before.

So, I'm just going to get in position.

That's it. Keep it pointing, just a bit lower. That's it.

-What do you think?

-That's a good position. OK.

Whew!

OK. Just open the gun now.

Feels nice. Got to tell you. Smells nice, too.

OK, so just push down on the stirrup latch.

-And that's it.

-That's the cartridge?

-It's ejected.

To establish a match between a cartridge and a gun,

what's crucial is what happens inside the gun

at the instant it's fired.

When the bullet's fired...

..there is very high pressure inside the cartridge case,

and that takes an imprint of this steel breech face

because this is a soft metal.

So, anything in this area

can leave markings on the cartridge case,

and those markings will be unique.

'm going to compare my cartridge

with another one fired from the same gun

using what's called a comparison microscope.

It allows you to examine two cartridges at once.

So, you've sort of overlaid one on the other...

-So that they should line up.

-..to make it incredibly easy for me.

So I can... I mean, I can definitely see it now.

Magnified and placed side by side,

it's easy to see that the two cartridges have identical lines.

These are caused by tiny imperfections inside the gun

created during the manufacturing process.

No two guns have the same imperfections,

so every time a gun is fired

it leaves its own unique imprint on the cartridge.

Such as the jockey-cap mark

that Churchill noticed on the cartridge found in the stolen car.

When Churchill fired Browne's gun

and examined the cartridge

he observed the same unique jockey-cap mark

and was able to tell the police

that Frederick Browne's gun was indeed the murder weapon.

But Browne claimed he was innocent.

He said a colleague of his, called Kennedy,

had given him the gun after the murder and not before.

When police arrived to arrest Kennedy

he drew a gun and tried to fire.

Luckily, the safety catch was on.

Both Browne and Kennedy were sent for trial at the Old Bailey.

Back in 1928,

the science of ballistics was unfamiliar territory for a jury.

Churchill presented photos of the jockey-cap mark

on the cartridge found in the stolen car

and also of the matching imperfection

inside the Webley found in Brown's possession.

His evidence was compelling.

The jury found both men guilty.

Kennedy and Browne were hanged.

The most eloquent witness had been the cartridge.

It had led the police to the murder weapon

and, hence, the killer.

The case of the jockey-cap killer put ballistics on the map.

For the very first time in an English court,

firearms evidence had been used

to secure a murder conviction.

Guns were no longer an anonymous way to kill.

SIREN WAILS

As forensic techniques have advanced, so have the criminals.

Nowadays, many would know not to leave bullets at a crime scene.

But in their quest to stay one step ahead,

ballistics experts are now using an exciting new piece of kit.

To show me how it works,

crime-scene analyst Mark DeGiovanni

has recreated the scene of a murder.

It's the case of US police officer Deputy Sheriff Jose Diaz,

who was shot and killed.

The gunman claimed that he had fired in self-defence

after Diaz had pulled his gun.

The case rested on whether his account was true.

And Mark has a piece of technology

that can help discover what really happened.

Firstly, what we have to do

is carry out what we call a laser-scan survey.

The 3-D scanner sends out lasers in all directions

to gather the detail of its surroundings

and build a virtual model of the scene.

In the Diaz case, the investigators used the virtual model

to work out the position of the gunman.

From bullet marks on the car,

they were able to recreate the trajectory of the bullet.

So, we don't get a straight line coming out of it,

we get a small cone with about a five-degree error

and we can see how that cone projects outwards into the scene.

They were able to prove that he was 70 metres away, behind a wall.

But the position of the gunman

didn't tell them whether he'd fired in self-defence.

The main issue in the Diaz case was actually the position of the victim.

To work out the position Diaz was in the moment he was shot,

Mark introduces a model of the body

with the exact path the bullet took through it.

What we're going to do is just bring them together

and analyse the two as one, really.

So, you have to get the body into a position

that realistically could have had a bullet enter it at that angle?

Absolutely.

The body is manoeuvred in the scene until the two lines of trajectory,

one through the body and one through the crime scene, line up.

Diaz was trying to take cover

and he was trying to sort of make himself as small as possible.

So this really does show conclusively

that this is the only position that he could have been at

in order for that bullet to have made sense, as it were.

Absolutely.

The 3-D laser scanner helped prove

that Diaz had been crouching when he was shot.

The suspect was charged with murder.

Thanks to 3-D laser scanning,

ballistics experts no longer need the bullet or cartridge

because they can piece together exactly what happened

simply from traces, like bullet holes,

that the weapon leaves behind.

But some investigators don't even have that much to go on,

because not all weapons leave a mark.

In fact, there's one that doesn't create evidence

so much as destroying it,

and it's something that most of us wouldn't even think of as a weapon.

Fire.

Arson is a brutal crime.

It's used to destroy property and, occasionally, to kill.

But fire is a risky weapon.

It's impossible to control.

It has a life of its own.

Yet, for a potential murderer,

fire has an important advantage.

It can be made to look like an accident.

John Lentini is an expert fire investigator.

In 1990, he received a call from the prosecutor's office

in Jacksonville, Florida.

They needed his help with a tragic case.

There was a fire in October of 1990...

..in which six people died.

Mrs Lewis, Mrs Lewis' sister,

and her sister's four children.

Mr Lewis, Gerald Lewis, survived,

as did his four-year-old son.

That was his only blood relative in the house.

SIRENS WAIL

Gerald Lewis had a court order to stay away from his wife,

and they had had a very rocky relationship

over the last six months.

So, yeah, he was the obvious suspect.

And in any fire like this,

where you survive and everybody else dies,

the survivor is the suspect.

So tell me about the position that he was in

at the time that you were called in.

Well, he was a defendant in a capital murder case.

He was charged with six counts of felony murder

and they wanted to send him to the electric chair at Raiford Prison.

Back in those days, Florida had this device called Old Sparky,

and they used it quite often.

And I was retained

to help Mr Lewis on his way to Old Sparky.

But Gerald Lewis had a defence.

He claimed that his young son had started the fire accidentally

while playing with a lighter next to the sofa.

So the jury were faced with one key question.

Was the fire an accident, or was it arson?

There's one piece of evidence that strongly implies

that a fire was started deliberately -

the presence of accelerant,

a substance like petrol or diesel that can be used to start a fire.

In the wreckage, fire investigators found clues

which, at the time, were considered proof

that an accelerant had been used -

charring on wood and distinctive marks on the carpet

known as pour patterns.

But while these patterns all pointed towards arson,

one vital piece of evidence was entirely absent.

There were no traces of accelerant at the scene.

There was no gasoline found in any of the samples.

In this context, a negative finding is an inconclusive.

So, at that point the prosecutor said, well, that kind of hurts,

and they wanted a second evaluation of the fire-scene inspection.

This was a high-profile case

and Gerald's life rested on the result.

We needed better evidence than what we had,

and the prosecutors agreed with that, they needed better evidence.

And so we were... We set up this test fire.

Lentini set out to test Gerald's story that the fire was an accident.

He recreated the scene in an abandoned house

identical to the Lewis home.

His idea was to set the fire going without accelerant,

just as Gerald claimed had happened on the night of the blaze.

Lentini expected the fire would burn far more slowly

and wouldn't produce any of the charring or pour patterns

found at the scene of the tragedy.

And this would establish it must have been arson.

But the test fire didn't go as anyone expected.

To reveal what happened,

I'm going to set up my own.

I'm with the Scottish Fire and Rescue Service

at this training facility in Edinburgh,

and we're going to carry out the controlled burn that Lentini did.

The difference is

that we're going to be using this specially designed hot-fire unit.

Helping me set the scene is Dr Rory Hadden,

a lecturer in fire investigation

from the University of Edinburgh.

We're mocking up a living room, as Lentini did.

With the room furnished and decorated

just as it had been before the blaze,

Lentini took a lighter and set fire to the sofa

just as Gerald claimed his son had done.

Lentini used no accelerant,

he poured no petrol on the floor.

The fire was started using a single, naked flame.

And then they watched to see what would happen.

It's actually burning quite clean in the beginning, but I can...

You can just make out now

-there's some kind of black smoke coming off?

-Yes, yes.

We're waiting to see

whether our fire will reach a crucial transition point

known as flashover.

The moment it goes from a fire in a room

to a room on fire.

Suddenly really scary, isn't it?

We can feel it, we're getting very close to flashover.

You can see that the coffee table has spontaneously ignited.

Flammable gases released from the furniture ignite,

filling the room with flames.

You can see you have the flames that are now coming outside of the room.

-That is a terrifying scene now.

-You can see how quickly that's grown.

This is for sure flashover, flashover has definitely happened.

Everything in that room is burning.

There's nowhere that you can be safe from that fire.

Back in 1990 when Lentini carried out his test burn,

the time a fire takes to reach flashover

was thought to be vital evidence.

Everyone believed that only a fire started using accelerant

could get to flashover quickly,

within a few minutes.

Without accelerant, they thought it would take much longer -

at least 15 minutes.

But the test burn defied all their expectations.

About three and a half minutes after we set the couch on fire,

the room went to flashover.

And when you observed that flashover was reached in just a few minutes,

that did what to your expectation of how fire worked?

It changed my view of what the cause of the fire was.

It rocked my world

and it changed my view of how to approach fires.

The fact that an accidental fire

could reach flashover in less than four minutes

was a shocking revelation,

one that completely overturned our understanding of fire.

And when Lentini ventured into the wreckage,

he discovered something else that he didn't expect.

There are one or two things that are quite interesting,

and one of them is, for example,

this charring on the table that we see here.

It used to be believed that, because this has charred at low level,

that must mean something was burning at low level,

particularly an accelerant.

However, now you see that it's just clearly an effect

of a post-flashover fire.

And in front of the bookcase, we find something else.

We have a patch of clean, almost undamaged carpet,

surrounded by a very sooty mark,

and that used to be considered to be evidence

of an accelerant being used - it's what they call a pour pattern.

However, as we saw, no accelerants were used

and we still saw this phenomenon.

The astonishing results of the test burn

changed the course of the Lewis case.

I was scheduled to be put under oath the next day,

and talk about how Mr Lewis' version of events

was not correct.

The prosecutors, by the way, were standing right next to me,

and I turned to them and I said,

"I don't think I can give a deposition tomorrow."

The prosecution dropped the case

and Gerald Lewis was released.

This case utterly transformed the way we interpret fire scenes.

Our beliefs about what was evidence of arson

were exposed as myths.

We now had to adopt new ways of investigating fire,

based not on assumptions but on science.

The case of Gerald Lewis highlighted just how difficult it is

to distinguish between an accidental fire

and one started with accelerant.

But, today, fire investigators have a new member of the team,

specially adapted to help.

Meet Gunner. He's one of Britain's fire-investigation dogs.

Gunner's a five-year-old Labrador-springer cross.

He's full of energy.

Always wants to work.

Gunner is often called to the scene of a fire

to search for traces of accelerant.

In this huge disused bank in Birmingham,

we're putting Gunner to the test.

We've added a couple of drops of accelerant to a cigarette end...

..set it alight...

..and then hidden the remains in one of the vaults in the basement.

The question is, will Gunner be able to sniff it out?

HE WHISTLES

DOG BARKS

Steady, steady.

DOG BARKS

Clive leads Gunner in a systematic search of the building.

Gunner has a secret weapon -

his nose.

It's some 10,000 times more sensitive than ours.

Nothing on this floor.

But what about the basement?

Suddenly, Gunner makes a beeline for the vault room.

Success!

Clever dog.

Having found the accelerant, he gets his reward - an old tennis ball.

At the scene of a large fire,

it's often impossible for humans to find accelerant.

But dogs like Gunner can detect even minuscule traces.

They can help identify cases

in which fire has been harnessed as a weapon.

Whilst fire is unpredictable,

the weapon that's most commonly used today is one of deadly precision.

And one breakthrough case for forensic science happened in 1942.

On a cold day in November,

at Witley Army Barracks in Surrey...

..Private Brown was on cleaning duty.

He had the unpleasant task of unblocking a drain.

As he reached down to pull out a wodge of soggy paper,

his hand fell on the blade of a knife.

He knew the police were looking for a knife

in connection with the recent murder of a young woman,

so he went immediately to hand it in.

The knife went straight to the pathologist working on the case,

Keith Simpson.

When Simpson saw the knife,

he instantly recognised its significance.

This is the exact knife that Simpson was given.

It had been lying in a drain for weeks,

and so it had no traces of blood or anything else on it.

To me, holding it in my hand now,

it's hard to imagine how Simpson would have known

that this was a murder weapon,

but he did know that.

How could he have been so sure?

Four months earlier,

a body had been discovered in a common close to the army camp.

Simpson was called to examine it.

Simpson smelled the body before he saw it.

Clearly, it had been there for weeks.

Three of the fingers had been gnawed off by rats,

the exposed arm had started to mummify

and there were maggots everywhere.

The body was so fragile

that Simpson insisted on digging it up himself by hand.

Most of it was unrecognisable,

but some of the clothing,

a tatty green and white dress, had survived.

Simpson gathered the body into a plastic sheet

to take back to his laboratory at Guy's Hospital.

Simpson's first question was identity -

who was the murdered girl?

He examined X-rays of her skeleton, the pattern of the teeth,

a few strands of hair and clothing found on her body,

and they all matched the description of a 19-year-old woman

who hadn't been seen for some time.

Her name was Joan Pearl Wolfe.

Joan had run away from home when she was just 16.

She left a strict Catholic upbringing

for a life spent drifting between casual jobs and temporary homes.

Joan had chosen Surrey

because of its large Canadian army base.

She'd been enticed by the freedom and romance

the foreign soldiers represented.

Simpson had established her identity -

now he needed to know how Joan had died.

There was no doubt it had been a violent attack -

her skull was in pieces.

Simpson found 38 major fragments

that had to be fitted meticulously back together.

Today, over 70 years later,

Joan's skull still exists.

It has been carefully preserved

and is exactly as it was after Simpson reconstructed it.

The most striking feature about this skull

is this enormous hole that's missing from the back of it,

and the radiating fracture marks which spread out from it.

And Simpson knew that a single blow from a blunt instrument

had killed Joan Pearl Wolfe.

But that's not all that you can see,

there are also these very curious marks on the skull, little holes.

There's one here, and another one on the top of the skull here.

These suggest that not only

was there a kind of horrible, violent killer blow,

but also some penetrating injuries

with a much smaller instrument.

Now, it's clear, just looking at this skull,

that a really nasty attack

took place on this victim.

Detectives investigating Joan's background

discovered she'd been engaged to a soldier called August Sangret,

a French-Canadian of Cree Indian descent.

He'd built Joan shelters in the woods where they could meet up.

Inside one of these shelters,

they found a letter from Joan to Sangret,

claiming that she was pregnant

and the child was his.

Sangret was brought in for questioning

and proceeded to give one of the longest witness statements

in criminal history,

running to over 17,000 words.

But, despite the excessive detail,

the police still didn't have enough to arrest him on.

Back in the laboratory,

Simpson turned his attention to the marks on Joan's skull.

It was clear to him

that they'd been made by a knife.

Now, these penetrating wounds on the skull aren't just violent,

they're actually curious -

they have a little slant in them.

And this told Simpson

something about the knife that was used in this crime,

because what he deduced

was that the little slants in the bone

showed that the knife that was used

needed to be twisted

before it could be removed from Joan's skull.

Simpson finally had some important information

to pass on to the detectives.

They needed to find an unusual knife with a hooked tip.

And a few weeks later,

Private Brown found just such a knife

hidden in the drains of the army barracks.

Now detectives needed to establish who the knife belonged to.

They got a break when an officer from the camp,

Corporal Harding, recognised its distinctive shape.

Harding had once been handed the knife as lost property

and had reunited it with its owner - Sangret.

In court, when the jury retired to consider their verdict,

they took the two fundamental pieces of evidence with them -

the skull and the knife.

On the 2nd of March 1943,

the jury delivered their verdict - guilty.

Sangret was hanged at Wandsworth Prison.

In the Sangret case, the knife led directly to the killer.

Today, the latest forensic techniques can use the knife

to determine more than simply who wielded it -

they can reveal how it was used,

a distinction that can be vital.

A common defence is that a stabbing was accidental.

The accused claims they slipped with the knife in hand,

or that the victim fell onto the blade.

Often, there are no witnesses.

The jury have little more than the accused's word to go on.

I've come here to the University of Leicester

to meet professor Sarah Hainsworth,

who has developed a test that can help establish

whether or not the person who's done the stabbing is telling the truth.

Sarah's expertise as a materials engineer

is frequently called upon to test a suspect's account of what happened.

Often, the accused will say

the knife caused more harm than they intended

because the knife was particularly sharp.

So, Sarah has devised a way to test the sharpness of the blade -

a drop tower.

So, what we have is a knife mounted here. If I simply release it...

Urgh! It's horrible!

Yes, I mean, the impact energy here is quite high

and the knife has penetrated right the way through this foam block.

And if you used a different sort of knife,

would you get a different kind of action?

So, if we used a knife that was blunter,

then it wouldn't necessarily penetrate

to the depth that this knife has.

Sarah has drop-tested hundreds of knives

and created a scale of sharpness that's used in UK courts.

But how sharp the weapon is is only half the story.

What the police are interested in

is how much force was used in a particular incident.

So, how hard was that knife taken

and pushed into somebody

to create those injuries?

So, to measure the force used in stabbing,

Sarah has built a device called a dynamometer.

What I'd like you to do now is to do a high-force stab,

so imagine that you've just had an argument with somebody

and really mean to stab them.

-So, sort of stabbing as hard as I can type thing?

-As hard as you can.

So, Richard will give you the countdown.

OK, in three, two, one, go.

It's sticking in a bit there.

Yes, so you've gone through the foam and into the backing slightly

and that recorded about 37 newtons,

so not the highest force.

So, I'm not a natural stabber, then.

No.

The greater the force used in a stabbing,

the less plausible that it could have been an accident.

So this measurement can help establish

whether an attacker intended to kill.

And this is what's driving the advance of modern forensics.

The latest techniques go beyond the facts of who, where and when.

They know try to tackle the more challenging questions of how...

..and why.

Criminals have always attempted to outwit those who seek justice,

but forensics is providing them with their biggest challenge yet.

Whether by analysing the victim's body,

or the murder weapon, or other forms of evidence,

forensic science is being used ever more successfully

to lead detectives directly to the killer.

Delve deeper with the Open University

and find out more about the science behind forensics.

Go to...

..and follow the links to the Open University.