Looking for a horror movie about a serial killer with an African mask

Question

This is a color horror/campy movie or TV movie that I began to watch when I was a kid (late 80s/early 90s). The movie was about a serial killer that recorded in film his own atrocities and messed up the minds of the police by sending the films to them as a gift. The killer wore a dark robe and a weird mask that looked like an African mask. He used a large knife to kill. He looked to me like a witch doctor or priest.

Among the characters, there is a policeman or detective that tries to catch the killer with the help of a female curator of an ethnography museum. At some point, the detective discovers, hidden in a subterranean chamber of the museum, a vintage (probably 60 years old) film reel that shows...

the curator looking exactly as she looks at the present day of the movie, which makes him to think that she is immortal which explains why she knows intricate details of the mask and modus operandi of the killer...

I don't remember the language but the movie had English subtitles. To me, it was a very scary movie and my parents never allowed me to continue watching. I hope someone here could help me to find this movie.

Answer 1

If the movie's orginal language was Swedish, it sounds possibly like Jonas Cornell’s Månguden (”The Moon God”), a 1988 horror film made for Swedish public television. According to a review:

Tomas Laustiola is John Vinge, a Swedish-Finnish cop that's responsible to catch a brutal serial killer. This unknown maniac slaughters innocent families out camping, with a HUGE machete. He or she is also dressed in a black robe and a creepy African mask, the mask of the Moon God. To really mess up the minds of the police the killer films his evil deeds and let the police have it as a gift.

which fits the main points of the question. The investigation indeed leads to an Ethnological Museum "where two mysterious researchers work". In case this jogs your memory, this is what the mask looked like: