My best guess is that they were stolen and later disposed of to get rid of the evidence, probably stolen in the burglary of a hardware store or something like that. Just a guess though. But I can almost assure you that they had some involvement in a crime or crimes.
You might want to check with your local county historian or historical society to see if anyone knows of any crimes from long ago that might fit with what you found.
Your local sheriff's office might have records of something that far back but not likely. The other option is to go through old newspapers from that period, but, speaking from experience, that could take years. Putting approximate dates on the pistols would definitely help.
Personally, I find all this fascinating. Where do you live, if I may ask?