Local police who were assigned by the Secret Service to help spot threats in the crowd at Donald Trump’s rally Saturday were inside the building where a gunman positioned himself on the roof to shoot at the former president, according to a Secret Service official briefed on the incident.

From inside the Agr International building, they spotted a man acting furtively, walking back and forth around the building with some gear, and radioed a Secret Service command post to alert them, the official said, speaking on condition of anonymity because of the ongoing investigation.

The revelations add to the growing list of questions about the Secret Service’s plan for securing areas outside the perimeter and about the failure of law enforcement to act quickly enough on multiple early warnings of suspicious activity. The Washington Post reported in a video analysis Monday that bystanders at the Trump rally in Butler, Pa., warned local police that they had seen a man clambering onto the roof of the building. A video posted to social media shows one man shouting, “Officer! Officer!” as others point toward the building. “He’s on the roof!” a woman says.

The account from a Secret Service official also underscores emerging tensions between that agency and local authorities over who is to blame for the fact that the gunman was able to access a clear view of the event. The Secret Service was responsible for the overall security plan, but the agency has said it relied on local law enforcement in areas outside the security perimeter. The Agr building was not inside the perimeter, which required members of the public to pass through a metal detector before entering.

The Secret Service official said the sniper team inside the building was from Beaver County, which neighbors Butler County, where Saturday’s rally took place. Local authorities said it was common for SWAT teams in nearby counties to supplement security for large events throughout western Pennsylvania.

The Beaver County district attorney’s office confirmed that a SWAT team from the county was at Saturday’s rally but declined to release additional information, pointing to ongoing investigations by state and federal authorities. In a written statement Tuesday, the county district attorney’s office said, “We are proud of the heroic actions taken by our officers.”

Richard Goldinger, the Butler County district attorney, said in an interview that the SWAT teams from his jurisdiction were all inside the secure perimeter. “Secret Service was in charge, and so it was their responsibility to make sure that the venue and the surrounding area was secure,” he told The Post. “That’s common sense I think. That’s their job.”

He added, “For them to blame local law enforcement is them passing the blame when they hold the blame, in my opinion.”

The BeaverCountian, a local news outlet, reported on Monday that counter-snipers were inside the building beyond the security perimeter for the event. The outlet reported that a Beaver County police officer warned a command center that he had seen a man with a range finder - a device the helps estimate distances - before gunfire erupted.

The Secret Service counter-sniper who killed the gunman, 20-year-old Matthew Crooks, had him in his sights and was trying to assess whether he had a weapon and was a threat, the official said. Secret Service radio traffic had relayed that local police either spotted or were trying to find a suspicious man around that building. The counter-sniper was a veteran marksman who is considered a legend in the Secret Service because of his high ratings for accuracy at long distances.

The counter-sniper who killed Crooks fired as soon as he saw Crooks lift a weapon, the official said. That counter-sniper killed Crooks in one shot, but seconds after he had fired at Trump, the official said.

The Secret Service’s advance security plan for addressing one of the main risks at the event - someone shooting from higher ground from outside the perimeter of the rally - was to have two teams of Secret Service counter-snipers stationed in front of the crowd, on the roofs of two barns behind Trump’s stage. The local counter-snipers stationed inside the Agr building were to provide “overcover” and surveil the crowd from the back and outside the perimeter.

Secret Service Director Kimberly Cheatle said in a television interview Tuesday morning that part of the reason the agency did not require a police officer to stand atop the roof of the Agr building was its slope. “That building in particular has a sloped roof at its highest point, and so there’s a safety factor that would be considered there that we wouldn’t want to put somebody up on a sloped roof,” she said. “So, you know, the decision was made to secure the building from inside.”

The roofs of the barns where sniper teams were located are more steeply sloped than the roof of the Agr building, a Post analysis of visuals from the event found.

The risk of an open line of sight for a shooter has been a security concern that the Secret Service has sought to address in planning for public appearances of presidents ever since John F. Kennedy was assassinated by a rifleman positioned in tall building in Dallas in 1963. Secret Service agents current and former have expressed shock that a gunman was able to get this close to the former president, an incident that is considered the most serious Secret Service security failure since the attempted assassination of President Ronald Reagan in 1981.

The Post’s video analysis shows a police officer in a black uniform looking up toward the top of the building. Crooks began firing two minutes and two seconds after the starting point of the newly published video, which begins with a man’s voice saying that people were pointing toward the roof. The shots began 86 seconds after the first audible attempts to alert police, according to the analysis, which synchronized several clips based on the sound of Trump’s voice over the public address system as he addressed supporters at a farm show grounds in Butler County.

The Post reported Sunday that the Secret Service relied on local police in Beaver and Butler counties to bolster its specialized tactical teams.

Evan Hill, Aron Shaffer and Maria Sacchetti contributed to this report.

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