The shot from the local officer caused the would-be assassin to temporarily recoil from his perch on a rooftop, according to the two officials and a Washington Post analysis of video evidence. Crooks’s retreat coincided with a 10-second pause in shooting, according to audio experts who examined the gunshots, a critical period that ended when the Secret Service countersniper shot and killed him.

It has been reported that a local officer fired at Crooks, but the analysis suggests that the officer may have played a more important role than previously known in responding to the attack at a July 13 rally in Pennsylvania.

One of the people who spoke to The Post, a local law enforcement officer close to the investigation, did so on the condition of anonymity because he was not authorized to speak publicly. The other, Richard Goldinger, the district attorney for Butler County, confirmed that a member of the county’s Emergency Services Unit (ESU), similar to a SWAT team, fired a shot at Crooks that prompted a reaction from the gunman.

“I don’t know if the officer actually hit Crooks and don’t believe he fired the neutralizing shot,” Goldinger, who oversees the emergency services unit, said in a text message. But Goldinger said he believed the officer’s shot caused Crooks to stop firing his weapon, buying the Secret Service snipers time to kill the gunman.

A third person familiar with the investigation, speaking on the condition of anonymity to discuss details that have not been made public, confirmed the Butler officer shot at Crooks before the Secret Service countersniper fired. The person said investigators have not found evidence that the local officer’s round struck the gunman, but witnesses said Crooks appeared to move after that shot was fired.

Ten shots were fired in the span of roughly 16 seconds, according to video recordings taken at the rally. Four audio experts consulted by The Post said the first eight shots, fired in bursts of three and five, have similar acoustic signatures and probably were fired by Crooks, who was armed with an AR-15-style rifle.

Eight spent cartridges were recovered on the roof Crooks fired from, FBI Director Christopher A. Wray told lawmakers last week. Trump’s ear was grazed by a bullet or bullet fragment, according to the FBI, and three spectators were wounded, one fatally.

Less than a second after the last of those eight shots, a ninth gunshot is heard. Then comes the 10-second pause.

The local law enforcement official close to the investigation did not know whether the local officer’s shot hit Crooks. But shortly after that shot, Crooks altered his positioning, the official said. Crooks stopped shooting at the rally site and slumped down behind the crest of the sloped roof where he was perched, the official said.

After the local police officer’s shot, “there was definitely some sort of reaction,” the official said. “Crooks slumped over, and he didn’t fire another round.”

The official credited the local officer with interrupting Crooks’s attack. “Anything that disrupts an active shooter can keep the situation from being significantly more catastrophic.”

The official’s account is supported by video taken about 100 feet west of the building from which Crooks fired. The footage was recorded by Jon Malis, a 52-year-old Pennsylvania resident who was watching the rally from that location, just outside the Secret Service security perimeter.

Crooks had roused the suspicion of local police as he milled around outside the rally with a golf range finder. They were looking for him when he crawled onto the roof of a warehouse complex and began shooting at 6:11 p.m. Malis’s video, first published by Fox News, records the sound of the eight shots from Crooks and then the sound of a ninth shot. After that ninth shot, the video captures Crooks as he turns, making his face visible to the crowd on the west side of the building, away from the rally, The Post analysis shows. He then appears to reposition himself.

The local officer who shot at Crooks was assigned to a barn behind and to the north of the rally stage, along with a counterassault and quick-reaction force team from Butler County, the local law enforcement official said.

The officer, who was not a sniper, had left the barn and was outside on the ground nearby when Crooks began firing from the rooftop about 110 yards away, the official said. The local officer saw the muzzle flashes from Crooks’s rifle, the official said, and fired his rifle at Crooks.

A rally worker told The Post they witnessed the local officer shoot at Crooks from the same location.

The worker, who spoke on the condition of anonymity because their employer had not authorized them to speak publicly, said they were standing behind the bleachers to the north of the stage when Crooks took his first shots. The worker said attendees scrambled while the local officer took aim.

“Everyone else was moving, and he wasn’t,” the worker said. “I remember thinking, ‘He’s not freaking out; he’s not yelling.’ He shot his gun, and I remember thinking, ‘We need to take cover.’”

A spokesman for the Secret Service said the FBI was best suited to answer The Post’s questions about the local police officer’s shot toward Crooks.

FBI officials confirmed that a Butler County officer fired at the gunman, and that the officer’s weapon has been taken to the FBI’s laboratory in Quantico, Va., for further analysis. Firearms experts at Quantico are also examining the gunman’s weapon, an AR-15-style rifle with a collapsible stock, and the weapon used by the Secret Service countersniper, FBI officials said.

FBI officials have said that a Secret Service countersniper fired the round that killed Crooks.

Malis’s video captures the 10th shot and Crooks’s subsequent collapse. “He’s down,” an onlooker shouted, according to Malis’s recording, which then zooms in to show Crooks’s body splayed on the roof.

The local law enforcement official told The Post that the Butler County officer was preparing to take a second shot at Crooks when the Secret Service agent shot him. The official confirmed there were a total of 10 shots: eight by Crooks, one by the Butler County officer and the last by the Secret Service.

Imogen Piper and Jon Swaine contributed to this report.