SACRAMENTO, Calif. (CBS13/AP) — Community members and activists gathered inside Sacramento City Hall on Thursday to protest the fatal shooting of an unarmed black man by police.

Black Lives Matter Sacramento organized the rally in honor of Stephon Clark, a 22-year-old who was shot Sunday night in his grandparents’ backyard, where he was staying.

The two officers yelled that they thought he had a gun in the moments before they shot him, according to audio from body camera footage released Wednesday by Sacramento police. But Clark was only holding a cellphone.

Footage from body cameras and an overhead helicopter does not clearly depict what Clark was doing just before police opened fire. Officers did not find a gun at the scene, and independent experts said the recordings raise more questions than they answer.

The officers appeared to legitimately believe they were in danger, several experts said, and if so the shooting was likely legally justified.

One officer is heard “doing a mental inventory to make sure there’s no holes in his body” because the officers appear to think Clark may have shot at them and missed, said Peter Moskos, a former police officer and assistant professor in the Department of Law and Police Science at John Jay College of Criminal Justice.

But Geoffrey Alpert, a professor of criminology at the University of South Carolina and an expert on police use of force, said the officers may have a tough time explaining why they jumped to the conclusion that Clark had a gun.

“The officers are going to have an interesting time explaining why they perceived they were in fear of their lives,” Alpert said. “It’s going to be a stretch.”

He also questioned why an arriving backup officer had the two original officers turn off the microphones on their body cameras, eliminating what he called “important evidence.”

Sacramento police did not respond to requests for an explanation or whether muting the microphones violated department policy nor why the officers waited five minutes to help Clark once he was on the ground not moving.

In an ideal world, the two officers should have immediately provided first aid, said Eugene O’Donnell, a professor of police studies at John Jay College of Criminal Justice. “But that could be more the product of hope than reality,” he said, with the officers still in shock and worried about their own safety.

The Sacramento Police Department said officers were responding to reports of a man seen breaking into at least three vehicles and later into a neighbor’s home. The police said deputies in the helicopter saw Clark break a neighbor’s sliding glass door before jumping a fence.

As a result, “their threat radar is really high,” said Plumas County sheriff’s deputy and special prosecutor Ed Obayashi, who trains officers and testifies in court on police use of force.

“They have to assume that their lives are in danger at that very second,” he said.

Sacramento Mayor Darrell Steinberg questioned police policies for providing medical aid after a police shooting, but said he can’t second-guess the split-second decisions of the officers.

He praised Sacramento Police Chief Daniel Hahn, the city’s first black police chief, for releasing the videos and other information promptly. Hahn has promised transparency and to work for better community relations since he took over as head of the department last year.

Steinberg said the department has improved its policies since the fatal shooting of a mentally ill black man in 2016, and said the council will address questions including the department’s use of force policies and training at a meeting April 10.

The shooting has ignited questions by relatives, activists and others.

Salena Manni, who identified herself as Clark’s fiancee, said he was the father of her two sons, ages 1 and 3.

“He would never want to leave his kids,” Manni said in an interview with ABC10. “I just tell them daddy’s always going to be with us, daddy’s in our hearts, always and forever. He’s always going to be with us. Don’t forget that.”

Clark routinely helped care for his grandparents at their home in south Sacramento, his cousin, Sonia Lewis, told Capitol Public Radio.

The department said the two officers have been with Sacramento police for two and four years, but each has four years’ previous experience with other law enforcement agencies. Both are on paid administrative leave.