Late 60s thriller about a young disillusioned man who is slowly planning to commit mass murders (inspired by Charles Whitman as well as a 1965 highway sniper attack). Boris Karloff plays a veteran horror actor (modeled after himself) who wants to retire but has to make one final appearance at his final movie's premiere at a drive-in theater, which is also set to become the final stage of the killer's murder spree, a clash between the classic on-screen monster and the real-life monster of modern society. It's a pretty fascinating thriller. The juxtaposition between the two storylines is very loose and can feel like you're watching two separate movies (story goes Roger Corman told Bogdanovich he could make whatever movie he wanted to make as long as he used Boris Karloff as well as footage of the Boris Karloff movie The Terror, which is probably the reason we don't get a story just about the sniper) but it's still well-written and well-directed, showing true promise of the then debuting Bogdanovich.
Btw, the James Brown the poster refers to is not
the James Brown, in case you're wondering.