The Fairfax County police officer who shot and killed unarmed motorist David Masters on Route 1 in 2009 has been fired for improper use of deadly force, police officials said on Tuesday.

The department confirmed that David Scott Ziants, 28, was the officer who was standing alongside Masters’s Chevrolet Blazer truck on Nov. 13, 2009, when it started to roll slowly away from him and several other officers. Ziants told investigators he thought one of the other officers had been struck, and that Masters was reaching for a weapon.

Ziants fired twice, hitting Masters once in the left shoulder with a shot that fatally pierced vital organs. The second shot grazed him. Fairfax Commonwealth’s Attorney Raymond F. Morrogh ruled that the shooting did not warrant criminal charges, but Fairfax police said a federal civil rights investigation into the shooting is continuing.

Police department observers could not recall an officer being fired for his involvement in a fatal shooting, and no Fairfax officer has ever been charged criminally in an on-duty shooting.

In January 2006, Officer Deval Bullock shot and killed unarmed optometrist Salvatore Culosi during an arrest for suspected sports gambling. Bullock was demoted from the SWAT team and suspended without pay for three weeks. Earlier this year, Fairfax County paid Culosi’s family $2 million to settle a civil lawsuit.

Gail Masters, Masters’s ex-wife and best friend, said Tuesday that Ziants shot her ex-husband “for no reason.”

She said Ziants “should have been treated the same way anybody would’ve who shot and killed somebody. He ruined [daughter] Courtney’s and my life.”

No civil suit has been filed in the Masters case, but David Masters’s sister and brother-in-law have filed notice of intent to sue. David Masters, 52, named his ex-wife and stepdaughter as executors of his estate, but under Virginia law only family members are entitled to recover damages in a wrongful death case.

Ziants declined comment Tuesday when a reporter knocked on the door of his Prince William County home.

His lawyer, Edward Nuttall, said he had not seen the findings and termination decision made by Fairfax County Police Chief David M. Rohrer, and that he no longer represented Ziants.

The officer was fired on May 6, Fairfax police spokeswoman Mary Ann Jennings said, after a nearly 18-month internal investigation. The internal investigation concluded that Ziants’s actions “were not in compliance with departmental policies on the performance of duty and use of force,” Jennings said. “The department’s use of deadly force policy is stricter than what is allowed by law. It prohibits the use of deadly force, except in limited circumstances, which were not found to exist when [Officer] Ziants shot Mr. Masters.”

Masters, a former member of the Green Berets, also suffered from bipolar disorder and had acted erratically shortly before the shooting, his ex-wife said. On the afternoon of the shooting, he had suddenly ripped some colorful flowers from planters outside a landscaping business on Route 1. The shop reported the theft to police and also noted Masters’s license plate, “FOO1.”

A lookout was broadcast for Masters’s Blazer. Around the same time, another case was reported involving a stolen car. When officers spotted Masters’s Blazer and pulled behind it, Morrogh said that Ziants, a U.S. Army veteran who had been an officer for six years at the time, mistakenly thought the Blazer was stolen.

An officer stood in front of the Blazer as it was stopped at Fort Hunt Road, another stood behind, and Ziants was alongside Masters, Morrogh said at the time of his ruling in January 2010. But rather than emerge from the vehicle, Masters rolled forward.

Ziants mistakenly thought the officer in front had been hit, though he had turned to walk back to his own car, and Ziants also wrongly thought Masters was reaching for a gun, Morrogh said. The prosecutor said Ziants did not have criminal intent in shooting Masters.

At the Fairfax County government center, the Virginia Citizens Coalition for Police Accountability lobbied on Tuesday for a role in overseeing such cases. Burton Rubin, the group’s vice president, said the Masters shooting was one of the reasons the group formed.

“An officer should not be using deadly force unless his life or someone else’s life is in danger,” Rubin said. “The police have a job — that’s to apprehend people and bring them before the courts.”