A mentally disabled girl was ruthlessly beaten by a group of teens in Chicago as bystanders cruelly laughed and recorded the assault, disturbing video shows. A 42-second clip posted to social media on Monday shows the girl, 15, walking with a group of several other girls and at least one boy when one of the girls suddenly punches her from behind. A witness who was already recording the teens walking then immediately starts laughing as the other girls — as many as five at one point — join the unprovoked attack. “They beating her,” one teen says while chuckling. The...