On December 13, 1933, the Dillinger gang executed an armed invasion of a Chicago bank, to empty its safe deposit boxes, netting the gang as much as $50,000. A day later, after Hamilton had left his car at a Chicago garage for some body work, the garage's mechanic called police with his suspicion that it was a "gangster car". When Hamilton returned to pick up the car and found a police detective, William Shanley and two other officers waiting to question him, he opened fire, killing Shanley, and managing to elude capture by the other two officers. This incident led to the Chicago Police Department forming a forty-man Dillinger Squad.