Samayoa activated his camera only after the shooting occurred, but since the device pre-records 30 seconds of video before it's activated, it captured images (but not sound) of the shooting.
Police have said they found no weapons on O'Neil, and attorneys representing his mother, Judy O'Neil, say there was no threat to Samayoa or a field training officer driving the squad car.
"In my view, this is flat-out deliberate, premeditated murder," attorney John Burris said at a press conference Tuesday. "There cannot be a clearer example of shooting an unarmed man without just cause than we have in this case."
He referenced video from Samayoa's body camera, which shows him draw his gun and appear to aim before O'Neil's head appears briefly in the frame.
"He did pull the gun out early and he sort of trained the gun, so to us that was a deliberate act, and the kind of deliberate act that says 'I’m going to shoot this person when he comes by, regardless,' " Burris said.
The Police Department did not respond to inquiries Tuesday about the lawsuit and duty status of Samayoa, who was placed on administrative leave after the incident per department protocol.
A spokesman for the San Francisco City Attorney's Office, which defends the city and its employees in civil litigation, said attorneys are reviewing the complaint and investigations into the shooting are ongoing.
"What we do know is that at the time of the incident, the decedent was driving a van that had been carjacked, the driver of the van had been assaulted during the carjacking, and the decedent was leading the police on a high-speed chase," spokesman John Coté said in a written statement. "The lawsuit admits that when the decedent finally stopped the van, he got out and ran toward the police car. A complete set of facts about the decedent and the incident will be available when the investigation is complete."
Despite O'Neil being unarmed, police officers have broad legal protections for using force if they perceive a threat, regardless of whether that perception turns out to be correct.
But Burris, who often sues California cities and police departments over fatal uses of force by officers, said the shooting was "one of the most shocking" incidents he'd ever seen.
He said his office had requested that the San Francisco District Attorney's Office and federal Department of Justice pursue criminal charges. The district attorney investigates all officer-involved shootings in San Francisco, but criminal charges in on-duty police shootings are extremely rare.
The complaint also alleges the Police Department failed to properly supervise Samayoa. Burris said that claim is related to Samayoa's field training officer, whom the attorneys identified as Edric Talusan.
"This training officer had ample time to request that the gun be put away, but in any event should have said, 'Don’t shoot unless we are in danger, or imminent danger,' and he didn’t do that," Burris said.
Charlie Grayson, Keita O'Neil's father, read a statement from Judy O'Neil that expressed "great warmth" and love for her son.
"I am wishing each time I look up I will be able to feel you watching over me," the statement said. "Until that time comes for me to be by your side, me and Charlie and your friends and family, we miss you."
"We're all going to miss him," added Grayson, who paused to wipe away tears as he read the statement. "It's pretty quiet around here."
Read the federal lawsuit below.