The shooting happened in the 3600-block of North Ashland at 3:30 Wednesday morning. It was caught on surveillance tape.
Police say the gunman approached the truck and opened fire, striking the driver and a passenger. The passenger was able to walk across the street for help.
A manager at the gas station says the tow truck driver would often park there overnight while listening to scanner traffic.
"I was shocked. When you hear this news, you don't know what to say. You just want to find out what's going on," said body shop owner Frank Wachaa.
The tow truck driver and his passenger are listed in serious condition at Illinois Masonic Hospital.