Very good explanation of false and true negatives and positives. Also of interest was ...
Quote
In the case mentioned at the outset of this article, police attempted to determine whether a human remains detection dog could detect residual odor from a decomposing body they suspected had been transported some time earlier in a rental car.
The rental car, a subcompact, was placed in a police parking garage that was filled with various police vehicles.
The rental car was the only non-police vehicle, the only subcompact, and had out of state license plates, facts which
the dog handler admitted to having noticed.
A film of the event showed the dog passing by the subject rental car without alert until the handler drew the attention of the dog to it again.
United States v. Anderson (E.D. Mich. Case No. 2003 CR 80602) Unquote.
The McCann rental vehicle was covered with Madeleine posters ... so hardly a 'blind' inspection.
Eddie was correct in the Parker case with his garage alert and the house next door alert. Eddie's skill is remarkable for detecting cadaver scent as Adrian Prout discovered.
We also saw video played in the courtroom to demonstrate how another dog, Eddie, found a sample pair of pants hidden in the Walker County Jail that was perfumed with a cadaver scent. Eddie is an English Springer Spaniel belonging to Martin Grime, a world-renown forensic K-9 expert based in the United Kingdom.
Grime testified he was paid $450 a day, plus travel and living expenses, by the FBI to search some areas in Walker County in connection with Teresa Parker's disappearance.
During a visit to Parker's home back in September 2007 Grime said he and Eddie sniffed around their garage.
"He immediately gave a positive bark response within the garage between a truck parked to the left of the entrance and a boat parked to the right," Grime said.
Grime added Eddie did not seem interested in the vehicles but in a scent that was wafting in the air, based on the way the dog held his nose upward. Grime said Eddie then "hit" on an abandoned house next door. Testimony shows that house was never repaired after a fire gutted the inside and killed a child several years ago.
During lengthy cross-examination Grime said there is no evidence to show Eddie smelled anything incriminating against or linked to Mr. Parker. Like Higgins, Grime said cadaver dogs can only prove useful when there is other evidence that corroborates the dog's "hits."
http://www.scentevidence.com/2009/07/dog-debate-at-center-of-murder-case.html