In The People Against O'Hara, director John Sturges seemed to want to cover some of the same territory that he had successfully traversed in Mystery Street the year before, using New York City rather than Boston as its setting (and some very effective location shooting). It has a bigger budget and a better cast, led by Spencer Tracy and John Hodiak, and James Arness is very good as a not-too-bright lug who gets himself into deep water. But it isn't quite as good a movie, mostly owing to the baggage that it carries in the script, including way too much backstory, which Sturges manages to convey rather clunkily. The first half, in which we are introduced to these characters, is rather heavy-handed, and Tracy doesn't seem entirely comfortable with the role in those scenes, although many other sequences are fine. The scene in which the police confront and pursue Johnny O'Hara through the streets of Lower Manhattan is practically the rehearsal for the pursuit of Richard Attenborough's character through the German streets in The Great Escape a dozen years later, but gems like that aren't enough to move the first half along fast enough. It's only when we get past the preliminary dramatics, in the middle and the second half, that the movie comes properly to life. The other "problem" with this movie, at least for viewers at the time, is the jaundiced view it presents of humanity; there aren't really any "heroes" in The People Against O'Hara, and no one to attach to emotionally until Tracy's character tries to achieve redemption. The prosecutor, played extremely well by John Hodiak, is a callously ambitious figure until his conscience is pricked by Tracy's debasement of his professional standing; and even Arness' O'Hara, for all of his good intentions, comes off as too stupid for words during most of the movie. This may all serve to make the movie realistic on that level, but it was also a difficult sell at the time, and the problems with the early segments make it all less than satisfying today.
On the other hand, there are some brilliant scenes in the movie. William Campbell's portrayal of Frank Korvac is one of the highlights of his career (and Campbell played many a criminal in his time, including some famous ones), and his scenes with Hodiak and Tracy, in and out of the courtroom, are phenomenal. That also goes for Tracy's scenes with Pat O'Brien, playing the chief investigator on the case. In addition, the use of actual New York City locales, everywhere from the court buildings on Centre Street to the streets underneath Manhattan's highways, gives the movie a bracing immediacy that almost overcomes some of the clunkier dramatic scenes in the first half. And there are some entertaining character and bit portrayals, including Julius Tannen and a soon-to-be-blacklisted Ned Glass, in some very important scenes. The movie was also extremely important in Sturges' career, for demonstrating that he could work well with the increasingly irascible Tracy, which enabled him to get the legendary actor, and get a great performance out of him, in Bad Day at Black Rock, which made Sturges' critical and commercial reputation.