Forensic science can involve absolutely anything,
anything in everyday life.
The main sorts of things I suppose we spend our time doing
are things like body fluids and tissues with DNA associated with them.
Obviously fingerprints are really important as well,
textile fibres from clothing and other furnishings,
glass and paint and other types of particulates.
Mobile phones and other digital media are increasingly important,
any kind of trace, you know, we can get involved in analysing and comparing
and then working out what it's likely to mean in the context of the case.
One of the most interesting kinds of evidence is textile fibres
because not only do they come in a wide variety
of different types and colours and so on,
so they can be very good evidence in themselves,
but also they can lead you to specific items in cases
where you really ought to focus your attention
and that then can lead you onto things like DNA
and marks evidence and all kinds of other kinds of evidence.
In the coastal path [murder] case there was some suggestion
that one of the key items we had there, a pair of shorts,
hadn't been worn by the suspect
but they'd been worn by another member of his family,
and there we were able to show through body fluids on the shorts
that actually there was DNA there that absolutely came from the suspect
but also came from his wife in the sorts of circumstances
that you might expect in a marriage, to put it nicely.
So we were able through that sort of thing to show who the wearer was
and confirm it in an interesting way.
Blood pattern analysis is an incredibly powerful form of evidence
for telling you what went on somewhere
so it's one of the first things you do at a scene where blood has been shed
is to have a look at the patterns the blood forms,
and there are lots of different things you can do.
I mean first of all using your eyes and thinking about it,
that's a very good start
and obviously photographing it so you've got a proper record of it.
And with blood patterns they tell you two main things:
they tell you what happened and the sequence of events at a crime scene
but they also absolutely point you
to where to go to sample for DNA profiling
to tell you from whom the blood came.
But DNA profiling is a quite expensive process
and so obviously you want to keep the number of samples
you send for DNA profiling down as much as possible
and you do that by understanding the pattern
and then by working out which samples you really do need to know
from whom the blood came.
There are lots of different sorts of
blood stain patterns that you get at crime scenes
and generally they tend to be combinations of some basic elements
and three basic sorts of elements:
first of all blood that's just dripped passively from a wound
so you get dripping and spotting and splashing from that,
and it tends to be the larger spots and splashes.
Then you can get blood spatter
where wet blood has been split up by some kind of force,
so in an extreme example it could be split up through gunshot,
slightly less extreme is if someone had been punching or kicking someone
then you get also this pattern of blood spots that are sort of finer
or less fine depending on the circumstances.
And then there are the bloodstains that arise through
contact between something with wet blood on it,
so you get sort of smears and swipes and wipes and those sorts of patterns.
But as I say normally blood patterns are a composite of
these different basic elements and the trick is really to work out
what you've got from these composite patterns.
Without doubt the most significant advance in forensic science in my career
has been the development of DNA profiling – absolutely without doubt.
It's transformed the strength of the link between
traces left on clothing, for example, and individual people.
The main kinds of samples that you take are the main body fluids
so they would be saliva, semen and blood.
But also very much these days, also skin flakes
and you get skin flakes off the surface of clothing
and off other surfaces obviously,
and there are a whole variety of different collection techniques,
depending on the circumstances, depending on the item and the amount of material
you think you might have - sometimes you can't even see it -
and they range from swabbing to cutting bits of material out
to removing the surface debris from an item
or the surface material from an item using sticky tape
and then cutting up the sticky tape into tiny bits
and so there's all sorts of ways in which you can collect DNA.
It's horses for courses and you just think of each case
and each item as you're doing it and what's the best way to get the DNA off it.
But then you have to be incredibly careful
that there couldn't be some innocent explanation for it
so you have to understand the context of the, for example, the crime scene
and the suspects relationship with the crime scene
if they'd ever been there before or they'd handled something that was found there.
You have to be really, really careful in interpreting
the findings from minute trace material.
So that's where the difficulty comes and potential accidental
contamination of items that you're looking at and you get results from.