A witness claims he warned security about a shooter on the roof just minutes before former US President Donald Trump was shot.

Yesterday (July 13) at around 6:15pm, multiple gunshots rang out while Trump, 78, addressed the crowd at an outdoor rally in Butler, an hour outside Pittsburgh.

Following the incident, Trump said he’d been struck by a bullet in the ‘upper part of [his] right ear’ and that he’d been taken to hospital after ‘much bleeding took place’.

Following his discharge from hospital, officials have confirmed that one rally spectator had died, while two others in attendance were critically injured.

All three of the victims were male, according to the FBI.

According to witness Greg Smith, he saw someone ‘bear-crawling’ up the roof and that he ‘had a rifle’.

“I’m thinking to myself ‘Why is Trump still speaking, why have they not pulled him off the stage’… the next thing you know, five shots ring out,” Smith recounted to the BBC.

“We noticed the guy bear-crawling up the roof of the building beside us, 50ft away,” he continued. “He had a rifle, we could clearly see a rifle.

“We’re pointing at him, the police are down there running around on the ground, we’re like ‘Hey man, there’s a guy on the roof with a rifle‘… and the police did not know what was going on.”

“Why is there not Secret Service on all of these roofs here?” he said. “This is not a big place. “[It’s a] security failure, 100% security failure.”

In a statement published Sunday (July 14) morning, an FBI spokesperson wrote: “The FBI has identified Thomas Matthew Crooks, 20, of Bethel Park, Pennsylvania, as the subject involved in the assassination attempt of former President Donald Trump on July 13, in Butler, Pennsylvania.

“This remains an active and ongoing investigation.”

An AR-style rifle was later recovered from the scene, but a motive for the shooting is yet to be confirmed, authorities said.

Earlier today, a Secret Service spokesman confirmed in a follow-up statement that agents had ‘neutralised the shooter’ and ‘quickly responded with protective measures’.

They added that Trump is ‘safe and being evaluated’.

Following the incident, Pennsylvania State Police Lt. Col. George Bivens released a statement regarding the shooter’s position outside the rally perimeter.

“It is incredibly difficult to have a venue open to the public and to secure that against any possible threat against a very determined attacker,” Bivens told reporters.

“That’s a huge lift to try to do.”