The police find a hotel key on the second victim, which leads them to one of the mobsters.

When she pulled back she showed him something in her hand, a hotel key with a bright orange tag.

He handed me a key, explaining it was his hotel key.

That is, Trenkler planned to return all his hotel keys except this one.

"Returning a hotel key is a simple matter," explained Cranston.

Gaudry forgot himself and brought the wrong hotel key here.

He spotted a hotel key in her briefcase just as she was snapping it shut.

She gave this to Cranston and said, "Sometimes a hotel key will work on other doors."

He dug his hotel key out of his pocket.

"I'm your husband," he said, and reaching in his pocket, he displayed a hotel key to my room.