Kevin Barlow was shot to death outside of a rail maintenance facility on 98th Street last week.
The rail union president said someone tried to carjack him.
Police are released images of a person they are looking for. He wore a gray-colored hooded top with a bear claw on the back and dark colored pants.
Cook County Crime Stoppers is offering a reward of up to $10,000 for information leading to an arrest.
Area Two detectives asked anyone with information to call them at 312-747-8271 or submit an anonymous tip at CPDTIP.com and use reference RD# JK312771.
Tips can also be submitted anonymously through the Crime Stoppers Tip Line at 1-800-535-STOP (7867).
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