8MM (1999) on Netflix

Private investigator Tom Welles is hired by the recently widowed Mrs. Christian who has found a startling pornographic film in her late husband's possessions. In the film a teenage girl is apparently killed and Welles is pretty sure it's a genuine snuff film. He takes the case, first going through records of runaways finally identifying the girl and learning that she may have run off to California. There he enters the seedy underworld of pornography with the help of Max California, a porn store clerk. His principal clue is the masked man who killed the girl as he has a unique tattoo on his hand. He soon finds the culprits but there is little satisfaction in resolving the mystery.