Police said a 30-year-old man was going into the Red Line station at Argyle near Broadway in Chicago's Uptown neighborhood on Aug. 15 when he was suddenly hit in the head from behind.
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CPD is asking for help finding the suspect, who is described as a 25- to 30-year-old man. He was seen wearing a gray shirt and baseball hat at the time of the attack.
Anyone with information is asked to call Area Three detectives at 312-744-8261.