Where does the phrase “to put the finger on someone” come from and What does it mean?

The American slang “to put the finger on someone” has a far different connotation than the older “to put (or lay) one’s finger upon something.”

The latter, though in general use the past hundred years, has the specific meaning, to point out, to indicate precisely; especially to show meaning or cause.

But the newer expression is gutter slang for “to mark a person for murder,” or “to accuse one of being a stool-pigeon,” or, somewhat with the older meaning, “to inform on a person.”