Ah! Brett, you may be right. I'll have to watch it again, but that would explain his presence. Not sure how he would have been able to just walk right in, however, as I would think it would still be a police crime scene. As a counter to that, though, is the fact that we don't see any tape up around the door, etc. The body outline, however, is still visible on the floor and Columbo is going there regularly. Plus, Devlin says to him, "I remember now, it (the "Ourselves Alone") was already there."