In Fritz Lang's M, Peter Lorre plays Hans Beckert, the screen's first serial killer. Beckert preys exclusively on children, a crime so heinous that the Berlin's thieves, safecrackers, and murderers band together to catch him.
And find him they do.
Lorre's Beckert is the polar opposite of the modern, urbane serial killers such as Hannibal Lecter or Dexter Morgan. Beckert is tortured, half in denial of the things that he does. His trial, even before a kangaroo court of criminals, finally gives him the opportunity to get it out, even if his audience are likely to be his executioners.
The speech he gives defined Peter Lorre's career for the rest of his life, and it's not difficult to see why. Lorre's portrayal runs the gamut from broken to manic in the course of one dead riveting, completely chilling, three-minute speech. Serial killers have become pretty old had old hat, but Hans Beckert's mad, harrowing speech remains a chilling landmark in cinema.