Prison dogs are trained more to institutional scent then specific human scent. I've worked with some prison hounds that when you gave them an item that contained the institutional scent with the human scent worked like a house on fire. But give them a "pure" human scent article and they did less well. Normally, they fizzled out at about the quarter-mile mark or at the end of a city block even when it’s known the subject left on foot. Most had trouble just getting out of the front yard. The ones of my experience are not trained for car trails (following subject scent coming from a motor vehicle). This is because once a subject gets into a car the speed at which they can travel far exceeds the speed of a on-foot team and they will never, ever catch up so from LE’s point of view, what’s the point? If the guy’s got a 4 hour head start that is later compounded by being in a vehicle there is no way that a dog working at 15-20 minute miles is ever going to catch up with a car traveling 50 mph. It’s also very dangerous for the trailing team due to the other vehicles also using the roadway even when you have marked units trying to protect the team.
When using trailing dogs (or any scenting dog) the answer is not always black and white but depends heavily on the skills of the individual team. What one team can do, another team may be unable. Not all dogs are created equal but must be judged as individuals. Handlers, too. And sometimes the handler doesn’t do the right job framing out to the dog what they want them to answer so the dog is confused about what you want them to do. Anyone who works a trailing dog never, ever stops learning.
Taking a dog to locations is a scent tactic under the broadly labeled category of “scent matching”. Scent matching is used to tie specific human scent to an object, location, or action. Here it can be a bit tricky and there's a few things handlers have to keep in mind. 1) has the subject been in that location before, recently, or within the scent timeframe the dog is trained for 2) has a close member of the family or significant other been at the location. If there is no reason for the subject to have been at that location then the dog, when taken to that location, should have absolutely no reason to indicate a matching scent in that area. The danger is that family/significant other can have that person’s scent on their clothing or vehicle due to their living in the same household and living together. This residual scent can be enough to trigger the dogs and give a positive indication even though the subject has not been there.
The other tricky half is that when you "drop" a dog to check for scent, you are dropping them into that area. They didn't work themselves there from the PLS. So you are placing them into the unknown. The dog CANNOT tell you “Oops, this is X number of days/hours old while that stuff back at the house was much fresher or only this old.” Now based on the dog/handler’s training and experience, the handler can sometimes draw a conclusion that the odor is “fresher” or “older” based on canine working behavior. If the scent is present and at a level the dog can detect then you will get a positive indication and sometimes the handler can have a good idea on the age but the handler has to be able to read their dog.
So by dropping dogs at locations where, for a variety of reasons, you believe the subject may have gone to then you do it because it can find you a loose thread that ends up as a valid lead.
Now scent age. If I'm on a trail and that person loops back over their same track, I expect my dog to abandon the older odor and cross over to the fresher track. The same can happen if they airscent fresher odor on the wind versus what they have on the ground. The dog will raise their head and work like an airscent dog following that odor to the scent source. (disclaimer: this is NOT TRUE for dogs trained as a tracking or non-scent specific patrol dog)
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