Creepy weirdo at my door.

I had a strange man knocking on my door yesterday morning. He claimed that he works for the rental company managing the apartment complex where I live. He said he was there to "inspect" the smoke and carbon monoxide detectors? Which are both working completely fine at my place. I told him I needed to see verification in regards to that because I never got a notice about that. He only showed me what looked like an old stack of papers. He looked dirty with tattoos and holes on his shirt. I said now isn't a good time. I didn't let him in. he said "I'll take your word for it" I suspect he was a killer.