Why reliance on sniffer dog evidence may throw us off the scent in trials

Almost a decade ago, a man was convicted and imprisoned solely on the basis of sniffer dog evidence, but could it have been a miscarriage of justice?

On the night on 11 January 1999, the occupier of a house in Stoney Barton, Westleigh, Devon, discovered an intruder in his house and telephoned the police.

A police dog handler who attended the scene later gave evidence in court stating that the animal had gone straight from the house and stopped beside a car parked half a mile away.

Inside it was Alvyn Oldfield, who told police that he had been sleeping rough in a nearby barn. He said that it was cold and he had sought shelter inside the car, which he found unlocked, and denied any involvement in the burglary.

Oldfield chose not to give evidence at the trial. The handler told the court that the dog had followed a track from the house and that it had stopped at the car because that was where the scent trail ended. There was no other incriminating evidence in the case.

In his summing up, the judge directed the jury to consider the handler's evidence "with circumspection" because a sniffer dog might not always be reliable and was not subject to cross-examination. These are the only directions a judge is required to give in relation to tracker dog evidence.

Research suggests that there are many factors that can influence the performance of a tracker dog. Unlike the direction given by a trial judge in relation to visual and voice identification by human witnesses, the jury is not told which factors may lead to error by the dog.

Andrew Taslitz, professor of law at the University of Pittsburgh, published a comprehensive analysis of the use of canine evidence in North America in 1990. He concluded that such evidence is imbued with mythical qualities about a dog's abilities and is likely to be overvalued, misunderstood and misused by jurors.

No mention was made in the judicial direction of the possibility that the handler may have been mistaken in his interpretation of the dog's behaviour. But the accuracy of dog tracking can only be appreciated through an understanding of the science of scent and the biology of canines. And police dog handlers do not claim to have any expertise in such disciplines.

The jury convicted Oldfield and he was sentenced to three years' imprisonment. In February 2000, he was refused permission to appeal. The court of appeal based its decision on the fact that the trial judge had followed the guidelines on tracker-dog evidence laid down in the case of Pieterson and Holloway (1995), by directing the jury to look at the evidence of the dog handler with circumspection.

In Pieterson and Holloway, the evidence of the tracker dog was peripheral to the prosecution case. In Oldfield's case, the dog handler's testimony was the only evidence to consider because the defendant chose not to testify.

It has taken several legal committee reports and a mountain of scientific research to bring miscarriages of justice based on visual and voice identification to light, and for appropriate rules to be drawn up on their admissibility. How long will it be before identification based on canine scent is subject to such rigorous analysis?

Amber Marks is the author of Headspace: On the Trail of Sniffer Dogs, Wasp Wardens and Other Dumb Friends in the Surveillance Industry

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