An internal Secret Service investigation has confirmed that multiple, substantial communication breakdowns preceded the 13 July attempted assassination of Donald Trump in Butler, Pennsylvania.

The Washington Post, citing unnamed officials, reported on Saturday that the former president’s security detail failed to direct local police to secure the roof of the building used by the gunman.

The Secret Service had discussed placing heavy equipment and flags between the stage and what would become Thomas Matthew Crooks’ perch
atop a glass factory 300ft away to block the clear sight lines from the roof.

But supervisors who arrived at Butler for the rally found cranes, trucks and flags were not placed in a way that blocked the line of sight.

Crook was later able to climb on to the roof and fire a rifle seven times, killing one spectator, wounding Trump in the ear and injuring two others, before being shot dead by Secret Service snipers.

The internal probe, known as a mission assurance investigation, found that unlike security details guarding a sitting president and vice-president that have military support, the Secret Service uses a command post separate from local police to protect political figures who are not serving in office.

But in Butler, Trump’s security detail had no way of communicating with local police guarding the perimeter of the fairground.

The astonishing lack of communication led to Crooks being able to get on the roof despite reports of a suspicious person carrying a rangefinder an hour before Trump was due to speak that were not relayed to the Secret Service. It took rally-goers to alert local police to a man “bear-crawling” on the roof before he loosed off shots at the former president, with one clipping Trump’s ear.

Instead, local countersnipers were instructed to text a photo of Crooks to just one Secret Service agent, and agents never heard local police radio traffic about trying to track him down. Butler county police also reportedly warned the Secret Service that they would not be able to post a patrol car next to the building but received no further instruction.

Kimberly Cheatle resigned as director of the agency days after the shooting after saying the roof’s slope was too steep for agents to manage. Acting agency director Ronald Rowe said in a statement to the outlet that “the Secret Service cannot operate under the paradox of ‘zero fail mission’ while also making our special agents and uniformed division officers execute a very critical national security mission by doing more with less”.

The report also found that the Secret Service had been slow to beef up Trump’s security even after it received reports of an Iranian plot to kill political candidates. Rowe testified to Congress later in July that he was “embarrassed” by security lapses and vowed to reform the agency’s practices. Two separate congressional investigations are also looking at security lapses.

The Trump campaign has said it has sometimes been forced to cancel or postpone events over concerns that security is insufficient and followed years of requests from Trump aides for greater security. Both the first lady, Jill Biden, and the vice-president, Kamala Harris, were in Pennsylvania that day, lending credence to claims that the Secret Service was stretched too thin.

“I think the American people are going to be shocked, astonished and appalled by what we will report to them about the failures by the Secret Service in this assassination attempt on the former president,” Democratic senator Richard Blumenthal told Fox News after being briefed on the internal review.