Example of a dog scent case (People v. Ryan Willis)

Ryan Willis was charged with the first-degree murder of his former girlfriend, Crystal Stahl. Several people witnessed Willis physically abusing Stahl while they were dating. After Stahl broke up with Willis, he told his friends that he would kill her by setting her taxicab on fire. A few weeks later, Stahl's charred body was found in her taxicab, which had been set on fire. 

During the trial, the state offered evidence that a bloodhound had detected Willis' scent at the crime scene. Willis objected, arguing that scent transfer unit (STU) technology was not scientifically reliable. The trial court admitted the STU evidence. Willis was convicted.

The Court of Appeal affirmed the conviction but ruled that the evidence should not have been admitted. The use of new scientific techniques at trial requires proof of reliability. The dog handler who testified for the state was not a scientist and, thus, was not qualified to establish that STU was widely accepted in the scientific community. There was no proof that the handler used correct scientific procedures while employing the STU. There were also several foundational weaknesses because it is unclear how long a scent remains on objects or whether each person has a unique scent. Thus, it was held that the trial court improperly admitted the STU evidence.

However, there was abundant evidence pointing to Willis' guilt. The Court of Appeal felt that it was not reasonably probable that the jury would have reached a different result in the absence of the STU evidence. Thus, the trial court's error was regarded as harmless, and the conviction was upheld. (People v. Willis (2004) ___ Cal.App.4th ___ , 2004 DJDAR 1010.)

The Willis case illustrates a number of issues. In all states, the trial judge rules whether evidence is admissible. When the evidence is supposedly scientific, California judges apply the rule announced in People v. Kelly (1976) 17 Cal.3d 24. The Kelly rule applies to new scientific techniques, especially in cases involving novel devices or processes. To protect the jury from scientific techniques that convey a misleading aura of certainty, a new technique must be subjected to a three-part test of reliability. First, there must be proof that the technique is considered reliable in the scientific community. Second, the witness testifying about the technique must be a qualified expert on the subject. Third, there must be proof that the person performing the test used correct scientific procedures. The analysis is needed where the evidence is so foreign to everyday experience that it is difficult for laypersons to evaluate merely using their own common sense and good judgment. (People v. Mitchell (2003) 110 Cal.App.4th 772, 782-783.)

The Court of Appeal in the Willis case found several things wrong with the STU evidence. The dog handler was not a scientist, so he was not capable of testifying that the STU was accepted throughout the scientific community. There was also no proof that the dog handler used correct scientific procedures while employing the STU. To make this evidence admissible, the court established a blueprint for prosecutors in the future:

[A] foundation must be laid from academic or scientific sources regarding (a) how long scent remains on an object or at a location; (b) whether every person has a scent that is so unique that it provides an accurate basis for scent identification, such that it can be analogized to human DNA; (c) whether a particular breed of dog is characterized by acute powers of scent and discrimination; and (d) the adequacy of the certification procedures for scent identifications. (People v. Mitchell, supra, 110 Cal.App.4th at pp. 791-792.)