now for over 20 years.

Although it can be really intricate

and time-consuming work,

it is just so fantastic when you actually make a match.

Most of us probably think that

we've got a pretty good understanding

of the basic principles

of forensic science.

We binge on true crime TV series,

we read and buy huge numbers of books,

and obsessively download true crime podcasts,

trying to figure out whodunnit.

But there are some things about forensic science

that you will probably only know

if you're an insider.

Let's start with some basics.

Where does all the information a forensic scientist needs come from?

Well, everywhere really.

In the early 1900s,

French criminologist, Edmond Locard,

declared that every contact

leaves a trace.

This forms the basis

of what is now called 'Locard's exchange principle'

which says that whatever you interact with,

you leave something behind and take something away.

One of the areas of forensic science where this is particularly applicable

is forensic botany.

There are around 390,000 different species of plants in the world,

each with its own pollen type,

and when it comes to crime scenes, pollen can really tell a story.

It's all around us, it's on the ground,

if you walk on soil or vegetation

you pick it up, inevitably you pick it up.

Patricia Wiltshire is a forensic ecologist,

she uses pollen to help solve crimes.

Unlike other forms of evidence,

pollen isn't easily washed away.

It gets into clothes and it can often be found on shoes

or on the foot pedals in cars.

Pollen and spores are too small to be seen by the naked eye,

so criminals rarely realise

that they've picked them up at a crime scene.

Pollen and spores are produced by plants and fungi.

They grow in specific places,

so you know very well that this plant will grow in this soil,

that plant will grow in that soil,

and because of that, we can predict where they are from.

In one particular case of an attempted murder,

this man tried to strangle a girl underneath a lamp post

and he said he hadn't been there, of course,

but by taking his clothing apart,

I showed that he'd bumped up against a fence with his left shoulder,

that he'd dragged her through a hedge,

that he'd knelt, and so on.

And because I sampled the crime scene in detail,

I could see where bits of his body had been

so I could actually reconstruct what he did at the time.

There are other ways in which nature can help forensic scientists

determine when a crime was committed.

Insects, for example, can provide a lot of information

if you know what to look for,

as forensic entomologist, Amoret Whitaker, explains.

When you die your body starts to break down and decompose

basically straight away. And so your body starts giving off certain odours

and those are very attractive to blowflies.

If we can work out how old the larvae are that are feeding on the body,

then we can work out the minimum time that that person must have been dead.

The colder it is, the slower the larvae develop,

the warmer it is, the faster they develop.

Really, the shorter the time span since the death,

the more accurate we can be.

Remember Edmond Locard, the French criminologist we mentioned earlier?

His contribution to forensic science

didn't end at "everything leaves a trace".

He developed and contributed to various methods of forensic analysis,

including dactylography, the study of fingerprints.

The interpretation of evidence has changed a lot

since I became a crime scene examiner 20 years ago.

Back then, if I examined a car whose door had been broken open

to gain entry, and the only evidence I found

was a fingermark on the outside of the driver's door,

I could reasonably expect

that if the fingermark was identified for someone,

then that person would eventually be charged with the offence

and the case would go to court.

However, things are now very different.

If the same fingermark was found today,

especially in a relatively non-serious case such as this,

there would be a strong likelihood that it wouldn't go to court

and this is because the Crown Prosecution Service, or CPS,

they need to be satisfied that there is sufficient evidence

to provide a realistic prospect of conviction.

Their argument for not prosecuting

based on the fingermark on the outside of the vehicle

might be that anyone could have walked by and leaned on the vehicle,

leaving the mark.

In the past,

defence barristers argued about who the evidence belonged to,

but now they focus on how the evidence got there.

Could the evidence have been left

by someone other than the person breaking into the car?

If there is any possibility it could be someone else,

then the CPS tend not to take these cases to court.

Forensic science is constantly evolving.

In the future, it's possible that many crimes will be solved

before they've even been committed,

as predictive software will mean that police forces

will be able to anticipate when and where a crime is likely to take place

and even who's likely to commit it.

Then there's our microbiome, the tiny microbes in our gut,

which, according to a new study Harvard,

can identify us as individuals just like a fingerprint.

Despite the rapidly changing world of forensics,

Linda says that there's one thing

that good forensic scientists never forget...

That we're dealing with real people's lives,

and we need to ensure that we work

in an objective and unbiased way,

because if we get it wrong, it's people's liberty that's at stake.