Photo from the personal archive of S.S. Podushkin

In the photo: East European Shepherd Douglas, in 3.5 years Douglas has apprehended 140 criminals.

Traces left by criminals at crime scenes can be visible (handprints, footprints, vehicle tire tracks, tool marks, blood stains, etc.) or invisible. Invisible traces at crime scenes include scent trails left by criminals at the scene of their presence, as well as on objects and items they came into contact with. Both types of traces are important for the successful use of detection dogs.
In turn, the handler, with the help of a search dog, in the process of working the criminal's trail, discovers new visible traces of the criminal and other material evidence (lost things or objects, crime weapons), thereby supplementing the initial data on the criminal.