REVIEW: When forensic science is caught red-handed

If you missed Incredible Evidence (C4), an extended edition of Equinox, don't worry: its findings will be coming soon to a police drama near you. The kernel of the programme's argument was that the evidence provided by forensic science is less rel iable than gullible juries routinely suppose it to be. If the majority of people need be concerned by these findings only in so far as they affect the next outing of Prime Suspect, their effect on the implementation of justice could be seismic.

The notion that wrongful conviction can issue from a DNA test is a disturbing new plot twist. The programme told of the imprisonment of a policeman in Largs who was found guilty of breaking into the home of and raping a neighbour and close friend. The victim insisted on his innocence, and at his trial oddly represented the most convincing witness for the defence. But a DNA test linked the semen samples from the accused with those on the dressing-gown of the victim, and down he went.

It is easy to see how juries can allow themselves to be blinded by science. The programme, which demonstrated that DNA testing, even when correctly performed, has a much higher chance of randomly matching samples from two people than was previously supposed, was obliged to get technical to prove its case. A few viewers could easily have lost the plot along the way.

Another case history called into question the technique of video enhancement from security video images. A tape of a building society armed robbery that was shown on Crimewatch led to an arrest. An image from the video, along with a photograph of the accused, was sent to a company that specialises in computer enhancement which proved that the images were of the same man.

A medical physicist argued that even when you measure from hairline to nose tip twice from the same image, the likelihood of getting an identical reading both times is minute. This left the tests looking pretty fishy, as they yielded precisely the same measurement from different images.

With fingerprinting, the third forensic field under suspicion, a similar type of uncertainty exists. No two fingerprints are ever identical, but a man was accused of rape because a fingerprint found in the blood at the scene of the crime was matched to his. Weeks later, the real culprit confessed, and the Lincoln forensic department would only admit that they "lost concentration". The over-arching argument of Hilary Lawson's compelling essay was that man can make fancy scientific tests, but man can alsomake bog-standard mistakes. As the programme did not neglect to show, human error can destroy its victims' lives.

It did, however, neglect to make capital out of the factor that plainly multiplies the chance of error. In the case of the DNA testing and the video enhancement, the victims of wrongful arrest had to cope with the Group 4 syndrome, in which individuals profit from law enforcement. The forensic testing for both was farmed out to private companies which cocked up. After initially lying, one refused to comment. The other no longer exists. It cannot be coincidental that the only culprit prepared to admit ontelevision that their error had cost a man his liberty was an employee of the state.

In The Ultimate Playboy (BBC 1), Jonathan Ross tackled Hugh Hefner, a man who has been interviewed so often that his answers are as silky as his pyjamas. Hef presumably knows that, like the dialogue in a porn flick, his words are mere captions, but what the hell. Previously one would have supposed that the grin permanently set into his jaw is the result of other bounties. Nowadays, it's plainly the smirk of a man who knows how much money he's just saved in free publicity, this time at the expense of theBritish Broadcasting Corporation.