Fritz Lang’s classic German film, “M,” was the originator of the modern serial killer thriller. One of the early films that had sound, this film has in many regards never been surpassed. It still ranks as the #55 best film of all time, on IMDB. You can watch the full film, for free, right here. Just make sure, if you speak English rather than German, that you click the “CC” button at the bottom of the video player, in order to get English subtitles.