The Macomb Daily reports the teen had vanished Friday after appearing in juvenile court in Mount Clemens on a probation violation.
Sheriff's deputies searched for about an hour until a security officer became suspicious when he saw a picture that had fallen to the ground outside judge's car.
A deputy checked the car and found the boy in the trunk.
Macomb County Circuit Judge Peter Maceroni says the teen likely used a button inside the unlocked car to open the trunk.
The judge says that from now on he will lock the car when he's at the courthouse.
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