...
... There is so much that is baffling about the Percy murder. If there were footprints in the dew from the murderer leaving the house, why was there none leading up to the house? I was struck by the fact that the killer went down into the water—not only could he ditch the bayonet, but, had the police thought to use tracking dogs, it would have been difficult or likely impossible to track the culprit. That would have been a very smart choice if the killer were from the neighborhood and had not used a car. (Yes, I’m another who believes Thoreson is likely the killer.) Unfortunately, the police didn’t call in tracking dogs for the Percy crime or the attempted break in in the neighborhood the night before....
It is possible that the killer took to the water in an attempt to avoid being tracked - either by dogs, or skilled human trackers. But unless he swam out to a waiting boat, he would not have fooled a good tracking dog by simply walking in the water for several yards - or even several hundred yards.
Unfortunately, as you point out, Tracking Dogs were not used in this case. That really is not too surprising, however, given the era and probably the level of experience of the police force regarding use of tracking dogs. Even today, it is common for a tracking dog to be brought to the scene after it has been walked all over and time has passed.
In a case such as this, rather than being a last hope "after thought" it should be one of the first things on the list to bring in a skilled tracking dog and handler.