When DH and I lived in Leeds, we had a flat by the university. Most of them were used by the lecturers/visiting academics, but there was one house with an older man who stood out. He'd stand outside and smoke, trying to chat to passing people.
DH always felt very uncomfortable around him; he snatched his violin from him once under the guise of asking to hold it. I felt similarly, but thought maybe he was just lonely as he was well spoken and seemed to have all of his faculties. I tried to be nice but cool, keeping hellos brief. He took a liking to me.
Stalking started. Someone left the main door to our building open, and he got in. The residents of the building decorated the hallways leading to each flat, and outside ours we'd put a coat rack, a table with flowers, and a few other bits. I came home to find my coat missing. It happened again, and this time he'd slid a note under the door asking for me to call him with a lot of suggestive innuendos.
DH went absolutely apeshit. Ended up stopping him from going around there, and we called the police. Gave the crime and name. They called back half an hour later telling me to stay away from him, he was extremely dangerous. I asked what he'd done and was told "we can't tell you, but implore you to cease all contact."
I don't known what happened but he wasn't there a week later.
Later found out from someone in DH's department that this guy was an arsonist, and he'd also been in prison for assault of minors. Seemed everyone but us knew as we weren't there long term.