Alternate versions

In the English and French language versions, in addition to having been dubbed, had some footage re shot. These scenes include the telephone conversation between the minister and the police commissioner, and the ending of the film. Peter Lorre's performance in the trial was re shot, however this time he spoke his lines in English or French, depending upon the version. The shots of him are lit and photographed much differently than Fritz Lang's original footage. Additionally, a shot of the police arriving was inserted, taken from an earlier part of the film (whereas in the original German version no police forces are shown at all). The court scenes have been eliminated and replaced with happy endings where young children play a game similar to the one seen in the opening (English) or a smiling couple watching their children play in the street (French).

When the US remake M (1951) was released, producer Seymour Nebenzal re-released the original film. For this re-release some things were changed: A new title sequence with music (Edvard Grieg's "In the Hall of the Mountain King") was added, as well as sound effects during some silent passages. In addition, the film was cut down to 99 minutes, removing i.e. any material that made the government look foolish.

Re-released in 1997 in the US on video; this version features the original ending, and new, computerized subtitles - beware of older versions with poorly translated, illegible subtitles.

A new, fully restored version premiered at the Cambridge Film Festival in July 2003. This version features a restored soundtrack, with Lang's originally intended long periods of silence, and the properly restored frame size. The film was previously altered with ambient noise on the soundtrack, and the frame drastically cropped around all four edges.

The version shown at the film's premiere (on May 11th, 1931, running time 110 minutes) had an alternate ending: it shows the full trial of the murderer. This ending was later replaced by a woman sobbing "Man muß eben noch besser auf die Kinder achtgeben. IHR..." (One must look out for the children even harder. YOU...)