If I know one thing about thieves, it's that they're trying to get something and get out before they get caught.
Waiting around while robbing someone is just asking to be caught. If someone hears or becomes suspicious, the police are just a phone call away.
When Nelly's Taqueria in New York was robbed, however, they decided to take a look at the surveillance footage. The camera didn't capture the robber's face, but it did show them something totally strange.