The gunman who tried to assassinate Donald Trump flew a drone above the site of the shooting ahead of time, law enforcement officials have told US media.
They say it remains unclear whether Thomas Matthew Crooks did this hours or days before the fateful rally in Pennsylvania on 13 July, reports CBS, the OceanNewsUK's US media partner.
Trump, now officially the Republican presidential nominee, has said he was saved "by luck or by God" when a bullet pierced his right ear during a campaign speech.
A spectator was killed in the attack, while two others were seriously injured.
Crooks, 20, was shot dead at the scene by Security Service agents, who have come under intense scrutiny over the precautions taken to protect Trump at the rally - held outside in the city of Butler.
Security Service chief Kimberly Cheatle has been summoned to testify before a committee of the US House of Representatives on 22 July.
First reported by the Wall Street Journal, investigators told CBS they were still trying to determine when exactly Crooks flew the drone.
They said they believed it was within days of the rally at the Butler Farm Show grounds.
Other US outlets, also citing security officials, claimed the device was flown above the area on the day the event took place.
The drone is thought to have been used by the shooter to pick the best line of sight for the podium where Trump was due to speak.
Crooks fired multiple shots from the roof of a building that was little more than 130m (430ft) from Trump.
In an interview with Fox News to be broadcast in full on Monday, Trump said nobody had warned him before he went on stage that there was a potential shooter.
"How did somebody get on that roof? And why wasn't he reported, because people saw he was on that roof," he said.
The drone - found in the gunman's vehicle after the attack - is now being examined by investigators.
Two explosive devices, a tactical vest, and four magazines full of the same ammunition used in the attack were also discovered in the shooter's vehicle.
The development comes as US Homeland Security Secretary Alejandro Mayorkas hit back at accusations by "some people" questioning the presence of women in law enforcement.
He praised "highly skilled and trained" women serving at every level "who risk their lives on the front lines for the safety and security of others".
Several female agents were part of Trump's security protocol during the shooting in Butler, shielding him after the shots were fired and leading him from the stage to a nearby security vehicle.
A number of social media users - including influential US conservative activists - later suggested that female agents were not best suited for jobs in the Secret Service.
"There should not be any women in the Secret Service," one such activist, Matt Walsh, wrote on X. "These are supposed to be the very best, and none of the very best at this job are women."
Some also criticised hiring practices that were focusing too much on diversity, equity and inclusion.
Mr Mayorkas said the Department of Homeland Security would "with great pride, focus and devotion to mission, continue to recruit, retain and elevate women in our law enforcement ranks".
"Our department will be the better for it, and our country more secure," he added.
