A man police described as a good Samaritan was shot and critically injured after he tried to break up a fight outside a Gwinnett County restaurant.

Witnesses told police two couples were having an argument shortly before 1 a.m. Saturday in the parking lot of the Tavern at Medlock in the 3200 block of Medlock Bridge Road.

When Thomas Rushworth intervened, one of the men involved in the argument shot him in the head, Gwinnett police Cpl. Deon Washington said Tuesday. Rushworth, 45, was taken to Gwinnett Medical Center, where he was listed in critical condition.

Washington said the alleged shooter and a woman were last seen running toward the County Club Village Apartment Homes, a complex behind the restaurant.

No arrests have been made yet.

“This is a very unfortunate situation and detectives are working very hard to apprehend the suspect who committed this senseless act of violence,” Washington said.

He urged anyone with information about the shooting to call police at 770-513-5300. Tipsters can also remain anonymous — and be eligible for rewards of up to $2,000 — by contacting Crime Stoppers at 404-577-TIPS or crimestoppersatlanta.org.