CHICAGO (CBS) — An 85-year-old man trying to catch a Blue Line train was injured and his wallet and credit cards stolen downtown on Thursday.

The victim and his 83-year-old wife, both from Des Plaines, had used the transfer tunnel between the Red and Blue Lines and was climbing the stairs to the Jackson stop when the attacker struck. Police News Affairs Officer Daniel O’Brien said it happened so fast that the victim’s wife only figured out when the thief bolted past her, her husband’s wallet in hand.

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The man told police his wallet contained about $40 and credit cards.

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He has been stabilized at Northwestern Memorial Hospital, with head and back injuries, and is cooperating with police.

O’Brien said the attacker is believed to be about 18 years of age, of medium height and build, and wore a black shirt and black shorts at the time.

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CTA personnel were reviewing its security video to see if the attack or attacker has been captured on video, and spokesperson Catherine Hosinski said whatever is found will be shared with Area Central Chicago Police detectives.