The detective, Columbo, had just arrived at the scene of the crime and found that the professor had been at the lab working for hours. He seemed to have electrocuted himself and ended up blowing the fuses for the whole building. Later in the night, the janitor came to clean up the lab and found the professor’s body. Columbo suspected the janitor, but when the janitor was questioned, he vehemently denied killing the professor. He said, “I came to work late. When I got off the elevator, I found the professor dead with his head on the lab table. I wish I could tell you more, but that is all I know.”
Then Columbo said, “I think you can tell us more at headquarters.”
Downtown, under grueling interrogation, the janitor confessed. What made Columbo suspect the janitor?