Body Double (1984) on Netflix

After unemployed actor Jake Scully finds his girlfriend in bed with another man, he moves out and accepts an offer from fellow struggling actor Sam Bouchard to house-sit for a few weeks. Apart from getting to live in a swank and ultramodern house he also get to watch a sexy neighbor, Gloria Revelle, who does a sexy dance in front of her window every night at exactly the same time. He becomes interested in the girl, infatuated even, following her around and eventually meeting her. She also has another admirer however and while watching her one night through his telescope, Jake sees her murdered by this other man. The police are skeptical about what he claims to have seen, but the case takes an even stranger twist when, while watching adult TV, he sees a porn star do the exact same dance he had watched for all those nights. He soon realizes he has been an unwitting accomplice in a complex plot.