According to John Boorman, Point Blank started when he met Lee Marvin in England. Marvin was there filming The Dirty Dozen; they had both read the script and hated it. But they did agree on one thing: there was a great character in Walker (a version of Richard Stark’s Parker).
Marvin had Boorman up to his hotel room and told him he wanted to make the movie with him under one condition, and Marvin through the script out the window. Boorman says that Mel Gibson’s version of Parker is very similar to that trash Lee sent flying. Perhaps Gibson picked it out of the gutters.