'Royal Family member' researched by Trump gunman just days before horrific attack

Thomas Crooks, aged 20, was killed by the US Secret Service after he fired at the former president at a rally in Butler County, Pennsylvania on Saturday.

Investigators told Congress that Crooks had searched online for various high-profile figures as he “scoped out” a target for assassination, including an unnamed member of the British Royal Family.

Crooks also searched for Christopher Wray, the director of the FBI, and Merrick Garland, the US Attorney General.

The shooting appeared to be planned just days in advance, as Crooks went to a local club the day before and practised on the rifle range, lawyers for the Clairton Sportsmen's Club confirmed to ABC News.

The 20-year-old purchased ammunition shortly before the incident, both online and in person, according to law enforcement sources.

He also asked his employer to take the day off on the day of the shooting but said he would be back as soon as the next day, sources have claimed.

Since Saturday's attempted assassination, FBI agents have been investigating Crooks's possible motive for the attack, including by downloading the content of two mobile phones he owned.

The devices contained images of Trump and Joe Biden, and the dates of both former president’s rallies and the Democratic National Convention, which will take place in Chicago next month.

This comes as the US Secret Service faces new accusations of incompetence over its failure to protect Trump, who escaped with an injury to his right ear.

The agency was alerted to a “suspicious person” in the vicinity of the stage an hour before the attack took place, and Crooks was ousted from the venue after setting off a metal detector.

Law enforcement sources told ABC News that Secret Service agents spotted Crooks on a rooftop 150 metres from the stage 20 minutes before he opened fire.

Several members of the public said they warned security staff at the event in the minutes before the attack, pointing out he had climbed onto a nearby roof and appeared to be carrying a gun.

Kimberly Cheatle, the director of the Secret Service, is facing calls to resign after she admitted agents had not stationed a sniper on the roof because it was too slanted and thought to be dangerous.

On Wednesday, she was accosted by senators at the Republican National Convention, who demanded an explanation for the security breach.

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A video posted online by Marsha Blackburn, the senior US senator from Tennessee, shows her and a colleague berating Cheatle explaining the timeline of the attack and asking why Crooks was not stopped.

She replied: “I don’t think this is the forum to have this discussion.”

Biden has ordered a full investigation into the alleged failings of the US Secret Service.