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Tracker dogs are occasionally used by the police to identify the perpetrators of offences. The dogs are trained to identify the odours left at the scene of the crime, and follow these odours to the perpetrator. Although there is not much case-law on this subject, the Court of Appeal held in R v pieterson (1995) that an identification made by a tracker dog is, in principle, admissible as evidence. To be admissible it would be necessary for the dog handler to describe the behaviour of the dog, and indicate how this behaviour was linked to the identification of the defendant.