The mother of a 42-year-old carjacking suspect who was shot and killed by a rookie San Francisco police officer this month has filed a wrongful death lawsuit demanding compensation for the “execution” of her unarmed son.

“Unreasonable and unjustifiable deadly force” was used in the Dec. 1 shooting of Keita “Iggy” O’Neil, who was fatally struck just below the neck on a Bayview street corner by a bullet fired by a police officer who had been on the force for four days, according to the suit filed Monday in San Francisco federal court.

“At this moment, I am hurting,” said O’Neil’s father, Charlie Grayson, in announcing the lawsuit at a news conference inside a church a few blocks from the shooting scene. “We are going to miss him.”

O’Neil had carjacked a California Lottery van on Potrero Hill by shoving the driver to the ground and was then pursued by police to the corner of Fitzgerald Avenue and Griffith Street, where he reached a dead end, police officials said. He got out of the vehicle and was running when he was shot by Officer Christopher Samayoa, who fired through the closed window of his police car as O’Neil ran past.

The lawsuit — which also alleges that an unnamed training officer sitting beside Samayoa was negligent for not preventing the shooting — seeks unspecified damages.

“It is without question a most shocking evidence of police brutality,” said civil-rights attorney John Burris, who is representing O’Neil’s mother, Judy. “It was not a panic shooting. It’s flat-out deliberate, premeditated murder.”

The nine-page complaint, which calls the shooting a “wrongful death (and) an execution,” says O’Neil was “unarmed and did not present an immediate threat to the officers (who) were still located inside the safety of the patrol car.”

The suit also alleges that “neither officer had their body cameras activated during the pursuit, a violation of department policy.” Samayoa turned on his camera after the shooting. But the camera had a feature that recorded 30 seconds of action before it was activated and captured the officer firing his weapon through the passenger-side window, hitting O’Neil as he jumped out of the stolen minivan and ran.

A spokesman for San Francisco City Attorney Dennis Herrera said the lawsuit was being reviewed but that O’Neil was “driving a van that had been carjacked, the driver of the van had been assaulted and (O’Neil) was leading the police on a high-speed chase.”

“The lawsuit admits that when (O’Neil) finally stopped the van, he got out and ran toward the police car,” said John Coté, a spokesman for Herrera.

Alex Bastian, a spokesman for San Francisco District Attorney George Gascón, said the case was “under investigation and there are no updates at this time.” The district attorney is in charge of criminal investigation of the shooting.

During a Dec. 7 town hall meeting at the True Hope Church on Gilman Avenue in the Bayview, San Francisco police officials played two videos of the shooting, prompting gasps and outrage from about 100 community members. While the shooting remains under investigation, Police Chief Bill Scott said the footage was released “for the purposes of transparency without drawing any conclusion during this stage of the investigation.”

Steve Rubenstein is a San Francisco Chronicle staff writer. Email: srubenstein@sfchronicle.com