The Last House on Dead End Street (1973)

After being released from prison, a young gangster with a chip on his shoulder decides to punish society by making snuff films. 

Infamous, hard-to-digest, lowest budget exploitation horror is actually made with quite some cinematic intelligence, and the grimy photography adds to the thoroughly malicious, disturbing atmosphere of the film, which is told from the perspective of the evil perpetrators; supposedly, this is a shorter version of a 3-hour long, but lost original cut - unimaginable to bear this in such a length.