Probably not innocent--almost certainly an accessory if not the actual murderer. Most of what I've read theorizes that the actual murder was committed by, or at least at the behest of, Anne Melton (since Laura would have exposed her to VD through Tom). So, whatever happened, it seems doubtful that his hands were entirely clean.

Maybe I should have said 'wrongly convicted' instead of 'innocent'. (It's often the case that the 'innocent' person was far from innocent, but was just wrongly convicted of a crime they didn't do.)