A mentally challenged man was sucker punched in the face as he walked down a street in the Germantown area of Philadelphia.
In a 30-second video which was recorded in slow-motion, a man is seen smiling before being distracted by a teenage boy who punches him hard in the face for now apparent reason and without warning.
The victim appeared to be in complete shock by the attack and was knocked backwards by the impact.
As the man attempts to walk away, he is then pounced upon by a second older man who punches him in the ear while another laughs hysterically at the beating.
All the men are clearly visible in the video but police do not yet know their identities and are hoping members of the public will come forward to help name and shame them.