2. an urban legend that the dark and atmospheric song (In the Air Tonight) which was such a departure from his usual work that it was actually a confession to murder.
The more common rumor about that song is that he witnessed something bad - a sexual assault, a murder, or someone allowing a preventable death.
The album was written just after his marriage broke, so some also thought it was a response to his witnessing his wife cheating on him.
None of which is true. He was just in kind of a dark place, and wrote some dark music for that album.