I can't believe no one has mentioned the photo

When Richard Basehart first goes to the apartment complex, he accidentally walks into Cyd Charisse's photo. I knew that was going to be the unmaking of his double identity.

The other thing that messed his "perfect crime" is that the pipe cleaner fell out of his pocket at Barney's place when he went for his handkerchief. The detective noticed the supply of pipe cleaners in his apartment, but other than that, it was never mentioned.