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A 19-year-old British man tried stealing a police officer’s gun to kill GOP presidential contender Donald Trump during a weekend rally in Las Vegas, according to a federal complaint filed Monday.

The complaint, filed by the U.S. Attorney's office in Nevada, identified the would-be assassin as Michael Steven Sandford.

Sandford faces one count of attempting to commit an act of physical violence on restricted grounds.

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He approached a Las Vegas police officer during a rally at the Treasure Island Casino pretending to ask for an autograph, the complaint says.

Asked about Sandford's detention, the U.K. Foreign Office said it was assisting after the arrest of a British national in Las Vegas. The suspect has a United Kingdom driver's license, according to the complaint.

After noticing the gun was in an unlocked position, Sandford grabbed the officer’s holster and the gun’s handle with both hands, the complaint says.

Sandford “reasoned it would be the easiest way to acquire a gun to shoot Trump,” the complaint says, adding that he “further stated that if he were on the street tomorrow, he would try this again.”

Sandford told a special agent that he had been in the U.S. for more than a year and lived in Hoboken, New Jersey, before traveling to Southern California on June 16 “to kill Trump,” the complaint says, adding: "Sandford had seen in the news a few days prior that Trump was coming to Las Vegas to speak."

The day after he arrived, the complaint says, Sandford traveled to a gun range in Las Vegas where, in an effort to learn how to shoot, he fired 20 rounds from a 9mm Glock, the complaint says.

The Trump campaign directed a request for comment to the Secret Service.

In a statement, the Secret Service said that unspecified additional charges were pending against Sandford. Citing an ongoing investigation, the agency declined to provide additional details.