Course, dog alerts are notoriously affected by the presence or otherwise of posters.
That & the handlers fashion sense.
The dogs passed the body farm tests with flying colours. That's why the FBI wanted them. This is what they're friend says:
Harrison also suggests that we use the skills of two totally remarkable dogs: the first an EVRD (Enhanced Victim Recovery Dog), achieves outstanding performance in the detection of human cadaver odour; the second, a CSI dog (Crime Scene Investigation) is capable of smelling the tiniest trace of blood, knowing how to recognise its human origin. To convince us of their capability and the extraordinary work carried out by these very special detectives in the course of over 200 investigations, he screens a video for us, showing their training and their intervention on the ground.
Eddie has been involved in a great number of cases, helping the police to resolve a good many riddles, thanks to his sense of smell. Even if the body has been moved, objects the body has touched have been contaminated by its odour, especially porous materials, fabrics, the upholstery in cars, etc. And that odour, Eddie knows how to recognise out of a thousand.
Keela, a scenes of crime specialist, is capable of locating particles of blood even after a place has been cleaned with chemical products or bleach. Sometimes, the residues are so microscopic they are missed by the instruments of the forensic police, as sophicticated as they are, and it's impossible to harvest them without taking all of what they are on.
Eddie is always the first to be brought onto a site. Once he has discerned the odour that he knows so well, it's Keela's turn to go into action, on the lookout for the slightest whiff of blood. The simultaneous presence of the two elements in a given place - blood and cavaver odours - is taken to indicate that a body has been there and that it's probably there that the death occurred.
The dogs' CV is impressive. Besides collaborating in hundreds of investigations, they passed the practical tests brilliantly at the FBI's "Body Farm," the only place in the world where human cadavers are used to simulate homicide scenarios and concealment of bodies. (TOTL)
