1960s American International (?) horror movie


Back in the late 1960s I saw a movie on television which I think was originally made in Italy for the American market, possibly by American International. A group of young people decide to investigate a supposed haunted house or castle. Once inside, they find a book of spells which indicates that crosses and stars of David confer protection from evil supernatural forces. Some of the young people then cast a spell, not expecting anything to happen. Unfortunately, they summon a demon and become possessed. There is conflict between them and their friends. The movie ends with the last of the "good" guys -- a man -- being killed with a stiletto or hypodermic needle by a passing stewardess -- one of the possessed girls -- in a crowded airport. She smiles as she walks away.

Thanks in advance.

Wow; I am impressed that you know such an obscure movie. Unfortunately, it isn't the one I am looking for. Thanks all the same.
It's actually not obscure. More infamous than famous though.

What you're describing sounds a bit like Equinox. Definitely not a perfect match, but just putting it out there.

Excellent suggestion; outstanding! Looking at the trailer available at IMDb and then the full movie you posted, I am absolutely convinced that the amateurs who made Equinox were inspired by the movie that I am trying to identify. So, I might well be able to do so by making a detailed investigation into Equinox.