Bystander Ken Cornell said a man -- who identified himself to police as Apperson -- came up to him, screaming, "Please call 911. ... I just shot George Zimmerman."
While Cornell did not see the incident or see Zimmerman, he described Apperson as a "shaken guy in his car."
Apperson told Cornell he didn't have a phone, so Cornell called 911.
According to Cornell, Apperson said: "I saw a gun and so I shot George Zimmerman."
Apperson described the incident as an "ongoing dispute," Cornell added.
Cornell said Appersons' "eyes seemed very shaken, his head was shaken. You could tell there was a problem going on."
Apperson could not be immediately reached for comment.
On Monday, Zimmerman flagged down an officer, saying someone shot at him and his car, said Bianca Gillet, a spokeswoman for the Lake Mary Police Department.
Zimmerman, 31, did not fire his weapon during the road rage incident, police said.
Zimmerman's attorney, Don West, said Zimmerman was driving into a retail center when a car came up behind him, flashing its lights and honking. Zimmerman claimed the other driver yelled at him, West said.
When Zimmerman tried to leave, West said, the other driver pulled up and fired a shot through the passenger side window of Zimmerman's truck. The bullet lodged somewhere in the car, West said. According to West, the other driver fled.
Zimmerman had a gun in the car but did not brandish it, according to West. Zimmerman was carrying the gun legally, the attorney said.
Zimmerman was briefly hospitalized and released a short time later.
The investigation into Monday's shooting is ongoing, police said, and officers did not know if any charges will be filed against Apperson. No arrests have been made in this latest incident.
Police confirmed that Zimmerman and Apperson had also been involved in a road rage incident in September 2014. In September 2014, the Associated Press reported that Apperson was stopped at a light in Lake Mary when a passenger in the car next to him started yelling, unprovoked.
The truck's driver, who Apperson believed to be Zimmerman, then reportedly said to Apperson, "Do you know who I am?"
Apperson pulled over, he said, and the truck followed him, blocking him in. Apperson claimed both men threatened to shoot and kill him, the AP reported. Apperson said he called police, but the truck was gone when officers arrived.
Two days later, Apperson said he saw Zimmerman outside his office and was worried Zimmerman was waiting for him, the AP reported.
Apperson declined to press charges at the time.
The Associated Press contributed to this report.