A Westbrook police sergeant is under investigation following an off-duty incident in Biddeford in which he allegedly drew his handgun on another man and shoved him through a store window.

But the officer, Detective Sgt. John Desjardins, says he was defending himself and his wife during a frightening, unpredictable confrontation with a man who was trying to yank open the passenger door of his car.

Desjardins was with his wife and a friend about 6:30 p.m. Tuesday when he pulled his car into a parking space on Main Street. They were headed for WonderBar, an Irish restaurant, where they planned to have St. Patrick’s Day dinner.

Brian McMahon, who manages Head Lines Barbershop and Salon at 193 Main St., said he was a few doors away from his business when he saw the car pull up.

McMahon says he thought his girlfriend was in the car, approached it and tried to open the passenger door. When he did, he says, the driver pulled a gun from the center console. McMahon said he backed up immediately with his hands in the air, but the driver then got out of the car.

“I say, ‘What are you doing? You going to shoot me?” McMahon said in an interview Thursday. “This man was out of control.” He said the driver, who flashed a badge and was identified by one of his passengers as a police officer, pushed him so that he fell into his large storefront window and broke it, but was not injured.

Desjardins said that as he pulled into the on-street parking spot, McMahon was suddenly at his wife’s door, trying to open it and screaming obscenities. Desjardins said his wife was terrified and he worried it might be a carjacking. He said he pulled a handgun from his center console, pointed it at McMahon and yelled at him through the window to get back.

“There’s a crazed-looking man trying to open her door,” Desjardins said during an interview Thursday. “I don’t know if he’s got a weapon.”

Desjardins said he put the gun in his pocket, got out of the car and identified himself as a police officer. McMahon retreated a few steps but then started yelling at him, the detective said.

‘NOW HE’S TAUNTING ME’

“I positioned myself between him and my wife’s car door. Now he’s taunting me by saying ‘You think you’re a tough guy with a gun,’ ” Desjardins said. “He’s so close, I can see the snot coming out of his nose.”

Desjardins said he shoved McMahon away, and he stumbled backwards and fell into the front window of the barber shop, breaking the window.

Following the incident, McMahon called police and Desjardins drove to the Biddeford police station and gave a statement.

The case has been referred to the York County District Attorney’s Office, which will determine whether criminal charges are warranted.

Biddeford police are also investigating. Biddeford Police Chief Roger Beaupre said he sent copies of the report to Westbrook Police Chief Janine Roberts, as well the York County District Attorney and the Office of the Attorney General, which is sometimes called in to investigate police officers. The district attorney’s office has asked for more information, he said.

Westbrook’s chief said Desjardins has not been placed on leave and she will wait for the complete report from Biddeford before determining whether to open an internal investigation.

“I believe Sgt. Desjardins was acting in self defense and in defense of his wife at the time of the incident,” Roberts said.

Roberts said she would open an internal investigation if a crime occurred or if an employee violated department policy. Officers are expected to behave off-duty as they do on-duty, she said. But when an officer is off-duty and points a gun at someone, the officer is not obligated to report it to his superior. The officer would be required to report it if he or she was on-duty, Roberts said. She said Desjardins and the people he was with were sober.

Roberts has only been chief since last fall but she knows of no similar incidents in Desjardins’ 19 years with the force.

Desjardins was one of two officers accused of using derogatory language by a female officer in a sexual harassment claim brought last summer against the Westbrook Police Department.

LENGTHY CRIMINAL RECORD

McMahon has a lengthy criminal history since moving to Maine, with 23 separate incidents, the most recent being two counts of theft and violating bail conditions in Westbrook in 2013, for which he received a suspended sentence. Other convictions include reckless conduct, robbery, burglary and multiple thefts. He has served time in jail.

McMahon said he thought he was the one under attack Tuesday and that he posed no danger to the officer.

“Anybody can clearly see if this man is in any kind of danger, why is he getting out of the vehicle? Why is he coming towards me?” he said.

McMahon said he wasn’t screaming, that he was on the telephone and was trying to be a gentleman and open the door for a woman he thought was his girlfriend. He said he couldn’t believe the driver pulled a gun, and he became upset about it.

” ‘Really? You’re going to shoot me over this? You’re that stupid?’ ” McMahon recalls saying. “Yeah, I called him stupid a few times.”

McMahon said he is 5’5″ tall and weighs 225 pounds. He said it took a powerful shove to send him reeling backward.

He said he hopes the surveillance cameras inside the salon captured the incident.

Desjardins said with nearly 20 years in police work he has never had a similar encounter.

“His behavior was so far out of the norm, it was scary to me and scary more so to my wife, who is not used to seeing things like that,” he said. Desjardins said he pushed McMahon because he wouldn’t back away. He said he thought McMahon was enraged enough that he might take a swing at him.

Desjardins said he knew when he pulled his gun that his actions would be analyzed.

“I knew instantly when I shoved him out of my face that was going to be scrutinized by Biddeford PD, my bosses and the York County DA,” he said. “My plan that night was not to be accosted by a crazed career criminal who didn’t want me parking where I was parking.”