Splitting hairs

French 16th-century jurist Bartholomew Chassenée's reputation was made by defending rats. The canon lawyer cannily argued that his rodent clients, who had been bizarrely charged under ecclesiastical law with feloniously eating up barley crops, should be excused from being tried because of the threat that would be posed to them during their journey to court by cats. So cats, ironically, saved the indicted rats.

But felines are now more likely to secure (human) defendants' convictions rather than their acquittals if the case of David Hilder is anything to go by. Hilder's manslaughter conviction at Winchester '¨Crown Court in July represents the first time cat hair has been used as evidence in England. '¨But is non-human DNA evidence a legal novelty? Or have 'furensics' brought people to justice before?

Eight hairs

When the torso of Hilder's victim David Guy was found on Southsea beach, investigators found eight cat hairs on the curtain the trunk was swathed in. The hairs matched Hilder's cat, Tinker. Hampshire constabulary swiftly commissioned forensic scientists at the University of Leicester to create a cat DNA database. The database comprised of samples from 23 cats from Southsea and 129 from other parts of the UK. Of 153 feline samples, only three matched the eight hairs found on Guy's body. Tinker's DNA type was, therefore, considered uncommon in the UK, and the DNA match was deemed significant.

Tinker, the Crown argued, placed Hilder at the scene of the killing of Guy or the corpse's disposal. Without even having to miaow on oath, Tinker helped to convict his owner.

The UK's cat DNA database is, however, not the first such repository for pet forensic information. Dr Wetton, part of the team involved in the Tinker analysis, had earlier created a database of British dogs' DNA while working with the now defunct state Forensic Science Service. The canine database was created because a dog might, when obeying his master's voice, reveal his master's vice.

Take the murder of '¨George Napier in 2001. Napier, '¨a doorman at southeast London's Paradise Club, was stabbed and killed in an attack involving Spencer Sheppard. Sheppard had set his pit-bull terrier, Colonel, on Napier during the melee. But Colonel, whose ear was sliced in the struggle, unwittingly peached on his master by leaving a trail of blood that led police straight to Sheppard's door. The Met's experts found that there was a million-to-one chance that the blood had come from a hound other than Colonel. Sheppard was subsequently convicted of conspiracy to cause grievous bodily harm. Whereas Sherlock Holmes solved a mysterious death in Silver Blaze because of 'the curious incident of the dog in the night-time' - the curious incident being what the dog does not do (bark) - it was '¨what Colonel did that was his owner's undoing.

Pedigrees and mixed breeds

And when DNA from dog hairs discovered on a corpse matched a dog owned by Daniel McGowan, he and three others were, in 2004, found guilty of the murder of Brian Keating (R v Khosa [2005] EWCA Crim 2918). More recently the murder of 16-year-old Oluwaseyi Ogunyemi in south London was solved using canine DNA traces left by killer Chrisdian Johnson's pit-bull terrier, Tyson.

But what is the scientific reliability of animal DNA databases? For a DNA match to be significant, a large comparison sample is required to ensure a reliable profile frequency and to ascertain the probability of a random match. While pedigree dogs and common breeds may be accounted for, many cross-bred, mixed-breed or outbred dogs might not be covered. And databases might not account for feral cat and wild dog populations.

Forensic zoology in criminal cases has yet, however, to be tested by this country's appellate courts, although appeals relating to dog DNA in the USA (People v Ige, Court of Appeals of California, Fourth District, Division One No D055893, 2010) and cat DNA in Canada (Beamish v. Her Majesty '¨The Queen, Supreme Court (Appeal Division) for the Province of Prince Edward Island (AD-0693 & 7/22/99)) suggest other common-law jurisdictions accept the reliability of non-human '¨DNA evidence. So cat burglars beware: your namesake might be your downfall. SJ