Four Flies on Grey Velvet

After wrapping up a recording session with his garage band, drummer Roberto (Michael Brandon) follows and confronts a mysterious stranger who has been stalking him to an abandoned theater where Roberto impulsively stabs him. A grinning puppet-like figure takes photos of the attack from a mezzanine box, which arrive in an envelope at Roberto's home the following day. It appears that he is being blackmailed, but it's not clear from whom or why.