Most police tracking dogs are trained for "disturbance tracking" and only a select few are capable of being trained for "scent descrinination tracking". Disturbance tracking is just that following the most recent disturbance not a specific scent. Criminals when they leave a crimescene are exuding adrenalin that can be tracked. Disturbed grass or tracks in the ground is another example.

Scent discrimination tracking follows a specific smell of skin cells that are constantly being given off from every person. These dogs have been known to follow this skin cell trail down the middle of roads that are given off thru the vent of the car the subject is traveling in. Forensic equipment like the STU-100 actually vacuum these cells from objects the subject has touched and transfer them onto a 4x5 inch gause scent pad.

For more information on this state-of-the technology visit: Public Safety Dogs, Inc.