The man was shot once in the chest, police said, just feet from his van.
Police will only say he worked in an office building nearby.
"It's just scary. I mean, I'll tell you, it's prayer time for everything and everybody," said a man who works with the victim. "I mean, you don't know who is around you, why they are. You gotta pray and be careful."
Security cameras are all around the building and security guards work inside.
The cameras likely captured the shooting. Police are using the video to help figure out exactly what happened Monday night.
"I think they need to put more security out here. I think that might help," said Juan Murray, of Oak Park.