There were times when Aldo the drug dog was not on his best form. He was trained to detect the presence of particular drugs, but sometimes he would say one or more of them was there when that was wrong, although on the occasion that concerned the United States Supreme Court there were other drugs present: Florida v Harris, USSC No 11-817, 19 February 2013.
What was the relevance of a record of false positives to the existence of probable cause for a search based on Aldo's indication?
Probable cause requires the kind of "fair probability" on which "reasonable and prudent [people,] not legal technicians, act": Illinois v Gates, 462 U.S. 213. The totality of the circumstances must be looked at, and rigid rules, bright line tests and mechanistic enquiries are inappropriate, according to Gates.
The Court, in a unanimous opinion delivered by Kagan J, considered that field-performance records may not capture a dog's false negatives or may markedly overstate a dog's false positives. This is because in the field – that is, in real-world performance – a dog's failure to detect drugs will often not be followed by a search and so the failure will go unrecorded. Similarly, an apparent false positive may in reality be a correct response to a residual odour or a small amount of drug that the officer failed to find. But evidence of the dog's reliability in a controlled setting, where errors are known, can provide sufficient reason to trust the dog's alert in the field.
All the evidence needs to be evaluated, said the Court. Here the facts supported a finding of probable cause because the defence had not contested the State's evidence that Aldo performed reliably in controlled settings. But where the defence did challenge the evidence of the dog's reliability the court should assess all the evidence and ask whether all the facts, viewed through the lens of common sense, would make a reasonably prudent person think evidence of offending would be found. "A sniff is up to snuff when it meets that test." Haw haw.
Here the problem with the Florida Supreme Court's approach was that:
"No matter how much other proof the State offers of the dog's reliability, the absent field performance records will preclude a finding of probable cause. That is the antithesis of a totality-of-the-circumstances analysis."
There may be other indicia of reliability, and absence of one sort may be compensated for by presence of another.
Because the defendant had not raised issues of Aldo's reliability at trial, he could not do so for the first time on this appeal.
"As the case came to the trial court, Aldo had successfully completed two recent drug-detection courses and maintained his proficiency through weekly training exercises. Viewed alone, that training record—with or without the prior certification—sufficed to establish Aldo's reliability."