Don't slam cops in 1948
This movie is interesting mainly due to the way it tiptoes around how the cops apparently actually railroaded someone in real life. I suspect if not for the way it gingerly treats what in 1948 must have been a touchy subject, it would have made for a much more entertaining movie.
As it was, I suspect this is the reason 'loose ends' that others have pointed out weren't addressed since it would have made law enforcement look even more inept and/or corrupt. They could have easily revealed Skutnik/Walush's motivations for lying (she ran a speakeasy and the cops coerced her to lie), as well as had an epilogue which explained that Zaleska/Marcinkiewicz was released five years later, additionally stating that both of them received handsome sums from the state for wrongful imprisonment.
In fact, it's the one thing that's really missing from the whole story, i.e., the people who were behind the framing. I guess the problem is that they all seem to have died by the time Wiecek/Majczek's mother had scraped together enough money to post her ad in the classifieds. If they had taken a little artistic license and kept one of them alive in the movie, i.e., a villian trying to foil McNeil/McGuire's attempts at getting to the truth, it would have been a better movie. The only one that comes close to this is whomever was interfering with McNeil's efforts to research the arrest records (and that individual is never revealed in the movie).