Peter Lorre [The Raven, The Comedy of Terrors] plays Hans Beckert, the child killer, with understated power and subtle emotion. It is one of the finest performances of Lorre's career I've even seen. Lorre portrays Beckert as the neighbor next door which, of course, is far more interesting than if he played it like Hannibal Lector in Silence of the Lambs. His final scene where he appears before the "court" is absolutely riveting. It is then, any only then that he reveals his true emotions for all to see. Brilliant!
M is supposedly based on the real-life case of serial killer Peter Kürten, the "Vampire of Düsseldorf", whose crimes took place in the 1920s, but Fritz Lang expressly denied that he drew any inspiration from the case. You might also find it interesting to know that during World War II the Nazi's would actually used his character's image as an example of how degenerates help to bring down civilized society. It's a prime example of life imitating art and much of this is due to Lorre's powerful presence on screen.
The print of M I watched is the restored version which was done around 2000. The picture is strikingly flawless for such an old film and the sound quality is excellent as well. The only thing that is missing is a soundtrack which was probably not a part of the original film. However, it is an interesting experience to watch a movie with periods of silence in it. We're simply not used to it in modern films. It serves as a reminder that a good musical score can easily enhance the viewer's experience of the film.
This one is a must see for fans of vintage horror. The direction, cinematography and editing are beautifully done and are way ahead of their time. A truly remarkable film.
As a final note Peter Lorre, who is Jewish, fled the country shortly after this film's release and Fritz Lang followed two year later. Both enjoyed long and respected careers in the United States.
For more info check out the film's entry in IMDB.