Ending...?

There's no twist, double or otherwise. There's a revelation at the end of the true killer's identity, which is no surprise to anyone who's been paying a modicum of attention. Near the end of the movie, the detective in charge of investigating the murders is in hot pursuit of the helmeted, motorcycle-riding killer. There's a brief chase, at the end of which the killer dies and is revealed to be the Professor, who was a main suspect all along. However, at the Professor's burial the detective confronts Miss Adjai (the Professor's lover) and says something to the effect that he hopes the ritual is over now, which is referring to the fact that Miss Adjai was the real killer all along. The Professor had also realized at some point that Miss Adjai was the killer, and at the end of the film he's dressed in the black outfit and helmet she wears to kill in order to throw the police off her scent and protect her. The detective, having no evidence of Miss Adjai's guilt, is forced to let her go, and we watch her stride away free at the end. Fade to black. I actually think this is a pretty decent and unique 80s slasher and can't believe it's rated so low, especially as compared with some of its genuinely horrendous contemporaries.

And, get the detective's cop buddy dressing up like the killer to scare the detective in the final scene. So...did he get the helmet and motorcycle suit off of Eleanor's boyfriend's dead body?

Questions, questions... :-)