Why didn't columbo pick up on the fact that frank staplin's fingerprints weren't on the other side of the fax paper like he did with George Hamilton in murder ca be hazardous?
Because it was irrelevant. Oscar Finch had nothing to do with the fax. It was the fact that Staplin was killed between sending the two pages that gave Columbo one more clue to prove it was not suicide.
Why would a man commit suicide between sending two jokes?