Dan "The Squealer" Mucelli was a known criminal with a reputation for violence. He had pronounced lips. After Kenneth Grebb was killed, Dick Tracy found documents implicating Dan Mucelli in involvement in a dope-trafficking ring. Anxious to get the papers away from Tracy, Mucelli and his associate Texie Garcia befriended Junior Tracy by giving him a job as a bread delivery boy.
When Junior discovered that the bread contained narcotics, he told Tracy, who confronted Mucelli. Mucelli turned off the lights, and shot Tracy twice. Junior was accused of the shooting because he was found with a gun in his hand. Using ballistics, Tracy proved Junior's innocence and then escaped from the hospital, catching Mucelli and using ballistics again to show that Mucelli was the shooter.
Later, Mucelli tried to escape from jail, but was stopped.