Somebody released an animal into the room that killed your colleague and then left.
Somebody outside the room was able to get your colleague's key from inside the room, unlocked the door, killed your colleague, then left and another person later locked the door from the outside.
Your colleague unlocked the door, somebody entered the room and killed him, then left and another person later locked the door from the outside.
Your colleague put his key outside of the room, somebody took the key, unlocked the door and killed him, then left and another person later locked the door from the outside.
Please repeat one of the following statements in red.
You found your colleague's key on his person when you entered the room.
You found your colleague's key in the room but not on his person when you entered the room.