[Jeff Higgins]

Connecticut has no handgun registration, so there is no way Vermont police could have used any such list to determine this doctor owned this gun.

Slides and barrels are not serialized components. There are no numbers on them. Only the frame, or receiver, is serialized and has any numbers stamped into them.

While the extractor certainly leaves a mark that may, in some cases, still be used to identify a particular gun, modern manufacturing has rendered most of them so uniform that this has become all but impossible. This really depends upon the age of the firearm, when it was manufactured. In the last decade or two, forget it - almost impossible to make a conclusive match. And, again, that is entirely dependent upon recovering fired cases in the first place. I bet they all remained within his truck.

Powder residue in the truck? Two years after the fact?

And, again, they did not recover the whole gun - the slide and barrel are gone. All they have is a grip frame. The doctor owes them no explanation for that. Plenty of hobbyists have gun parts and incomplete guns laying around. If it was his only gun, that is kind of weird, but he still owes them no explanation.