>> reporter: concerned, marissa walked down the hallway and listened in. >> i knocked on the door and waited a moment, and then i definitely heard a click, like a lock. i had the feeling that there was somebody on the other side of that door. >> reporter: she called potsdam pd. >> i live in 3a, and they live across the hall. it just made me a little nervous that i thought i heard yelling and then i knocked to see if they're okay and then it was silent. i'm sorry if it's not anything. it was a weird situation that it makes me uncomfortable. >> okay. i'll have somebody check on it. >> reporter: a patrol officer arrived at the second-floor apartment around 5:15 pm. no one answered his knock, so he waited for the building manager to bring a key. >> the patrolman hears what he thinks is footsteps moving inside. >> reporter: inside? >> inside the apartment. and then they get the key. they open the door. and they go inside. >> reporter: everything appeared to be in order. the living room was tidy,