How much truth there is in this "true story" with "real people" is a question best left to historians of organized crime. The subplot of Stuart Whitman ("Joey") and May Britt ("Eadie") as a loving couple caught up in nasty doings certainly seems like the stuff of fiction. In any case, this is a low-budget "B" picture with limited resources for portraying the 1930s setting and documenting the historical events with authentic detail.
The one extraordinary element in the movie is the performance by Peter Falk as a contract killer. He is not only completely believable in the role but downright original, giving us a character who is merciless and vicious yet quick to take offense if anyone finds this objectionable. He can sound plaintively sincere even as we quickly come to see that he is incapable of sincerity. He has a host of minor quirks and tics that are fun to watch.
Face it, evil can be fascinating and even attractive, in a disturbing way. Another example in this movie is the portrayal of crime kingpin Louis "Lepke" Bucholter by David J. Stewart. While certainly not achieving the high level of Falk's performance, Stewart shows real style as the milk-drinking mobster.
There is one other bonus in this film: Sarah Vaughan, looking young and pretty, sings a nice song with that inimitable voice.
