For me this would be the Blackout Killer, which is a serial killer during the second world war who killed 4 women, and attempted to murder an additional 2, over a period of six days in February 1942.
The story has it all; a war veteran, murder, war, a kickass name, the dark streets of London, really all an exciting movie needs.
What are events or stories that you think should be made into a movie?