DNA tests that take minutes, software that identifies the baddie on CCTV footage, and suspects confirmed from prints on the glass left behind at the crime scene, are all common scientific crime-solvers in TV forensic dramas like CSI and Silent Witness, but the real forensic scientists cringe at the miraculous nonsense that their fictional colleagues get away with.

 

Face recognition

 

As Nigel Allinson, Professor of Image Engineering at Sheffield University puts it, ‘Yes, we can put a man on the moon if we try very hard, but whizzing around the galaxy at warp factor 10 is totally beyond us.  What TV forensic scientists do is often science fiction.’  Take face recognition software. ‘When the subject is cooperating, looking directly into camera against a blank background like in a passport photograph, we might hit 90% accuracy this year,’ says Nigel.  Even using a PC webcam and looking directly at the camera, is enough to reduce the software’s hit rate to 50%.  The cluttered background of your bedroom or office is enough to confuse it, ‘Throw in a real criminal who wants to avoid the camera and it hasn’t a chance.  We still need people to sift CCTV tapes in important cases’

 

Humans are very good at recognising faces even from limited information.  You can recognise someone you know even though you can only see them poorly, but it is very hard to construct software that will do that.  Psychologists say that our ability to recognise at most 500 – 600 people is limited by the maximum size of prehistoric tribes and we are asking machines to do much, much better than that from millions of images.  Face recognition software was installed by one of the London boroughs experimentally on their CCTV system recently.  It pulled up so many false positives (cases of mistaken identity) that it was abandoned as next to useless.

 

The virtual crime scene

 

One step ahead of the TV shows, researchers at Aberdeen’s Macaulay Institute are developing a virtual reality crime scene theatre.  This means that the real crime scene is recorded in minute detail, but less people have to visit and possibly contaminate it.  The crime scene can be shared with many experts and even accessed by video conferencing remotely.  In cold cases it will be an aid to visualisation of a scene that may no longer exist.

 

 

Fingerprints

 

Fingerprints always feature as key pieces of evidence on TV, able to definitively point the finger at the wrongdoer.  Far from being foolproof, the national success rate in finding the villain from fingerprints left at the scene is less than 10 %.  Fingerprints are unique to the individual, and are laid down before birth.

 

‘In an ideal world we would have a clear print to use, but much of the time when people touch surfaces, only part of the fingertip makes contact, or it is smudged or smeared, or the touch was so light that little detail is recorded,’ says Sue Jickells, a researcher in forensic science at King’s College London, ‘A tiny part of a print is much more difficult to match up because there are less unique marks and ridges to use.’  Many prints at the crime scene are latents - not visible to the naked eye, which is why you see the scene of crime officers or SOCOs with torches trying to pick them up.  If that fails, SOCOs use brushes and powders to show up prints. The next step is to use more esoteric techniques such as the ‘superglue’ cabinet’.    Dorothy Gennard at Lincoln University describes the process, ‘Whatever you are testing for latent prints is put into the superglue cabinet, let’s say its a bin liner.  Heat vapourised superglue is passed over the bag, and the superglue binds to fatty deposits in the fingerprints making them visible.’  But even with sophisticated techniques like this, investigators are in trouble if the perpetrator is one of the small proportion of the population who have no fingerprints.  Chefs burn their fingerprints off most of the time in the course of their work, and manual labourers just wear them off.  

 

The Brilliant Loner

 

Sue, Dorothy and Jim Fraser, Professor of Forensic Science at Strathclyde all say they rarely watch the likes of CSI and Silent Witness because of the gulf between real life and the TV shows.  ‘It’s always one individual who plays a super detective, brilliant scientist, perfect pathologist rolled into one and who is virtually infallible. Reality is all about teamwork and slow, painstaking and meticulous work,’ says Jim, adding, ‘TV detectives like Dalziel and Pascoe are forever traipsing on to crime scenes in everyday clothes, that would never happen, because fibres from their clothes would contaminate the crime scene.’  The TV producer’s problem is that the full bodysuits normally worn to prevent this are not that photogenic.  Jim also has a laugh about the scene of crime photographers on TV who seem to get their jobs done in seconds, ‘To record a crime scene thoroughly at a typical 3 bedroom house takes at least two hours.’  The real life team in a murder investigation is a minimum of 12 – 15 people, many of whom are scientific specialists.