BBC Verify has analysed video which shows the police were warned of the threat to Donald Trump almost two minutes before Thomas Matthew Crooks opened fire on him from the roof of a building at a rally in Pennsylvania.
Mr Trump narrowly survived the assassination attempt, after the gunman accessed a roof around 130 meters from the podium where the former president and Republican candidate was speaking.
It’s the job of the US Secret Service to protect sitting and former presidents. Somehow the gunman managed to breach the security perimeter with a rifle and reach an elevated position close to Mr Trump.
Video of the attack and the accounts of eyewitnesses appear to show that members of the crowd became aware of the threat before the police and other security officials alerted them to the danger.
When the gunman opened fire security and Secret Service officials at the rally reacted to the threat and responded, with Thomas Crooks shot dead by snipers.
Clive Myrie presents BBC News at Ten reporting by Ros Atkins and Frank Gardner.
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