Jawaun Dontell Woods is charged in the attack but has not been caught.
A car stolen during the November 26 incident was recovered in Indianapolis.
Investigators say a surveillance camera at a gas station in the area where the car was found captured video of Woods.
Police consider Woods armed and dangerous.
The victim was cut on his neck and hands as he was waiting for his wife to arrive on a South Shore Line train.
Police say Woods took the victim's keys, wallet and car and then allegedly went to a Wal-Mart and bought three Lady Gaga CDs with the victim's credit card.