WASHINGTON (AP) — A man who authorities say staked out Donald Trump for 12 hours on his golf course in Florida and wrote of his desire to kill him was indicted Tuesday on an attempted assassination charge.

Ryan Wesley Routh had been initially charged with two federal firearms offenses. The upgraded charges contained in a five-count indictment reflect the Justice Department's assessment that he methodically plotted to kill the Republican nominee, aiming a rifle through the shrubbery surrounding Trump's West Palm Beach golf course on an afternoon Trump was playing on it. Routh left behind a note in which he described his intention, prosecutors said.

Court records show the case has been assigned to Aileen Cannon, a Trump-appointed federal judge who generated intense scrutiny for her handling of a criminal case charging Trump with illegally hoarding classified documents at his Mar-a-Lago estate in Florida. She dismissed that case in July, a decision now being appealed by special counsel Jack Smith's team.

The attempted assassination indictment had been foreshadowed during a court hearing Monday in which prosecutors successfully argued for the 58-year-old Routh to remain behind bars as a flight risk and a threat to public safety.

They alleged that he had written of his plans to kill Trump in a handwritten note months before his Sept. 15 arrest in which he referred to his actions as a failed “assassination attempt on Donald Trump” and offered $150,000 for anyone who could “finish the job.” That note was in a box that Routh had apparently dropped off at the home of an unidentified witness months before his arrest.

After the attempted assassination, the person opened the box, took a photograph of the front page of the letter — addressed “Dear World” — and contacted law enforcement.

Prosecutors also said Routh kept in his car a handwritten list of venues at which Trump had appeared or was expected to be present in August, September and October.

The charge of attempted assassination of a major presidential candidate carries a potential life sentence in the event of a conviction. Other charges in the indictment include assaulting a federal officer, possessing a firearm in furtherance of a crime of violence and the two original firearms charges he faced last week.

The potential shooting was thwarted when a member of Trump’s Secret Service protective detail spotted a partially obscured man's face and a rifle barrel protruding through the golf course fence line, ahead of where Trump was playing. The agent fired in the direction of Routh, who sped away and was stopped by law enforcement in a neighboring county.

Routh did not fire any rounds and did not have Trump in his line of sight, officials have said. He left behind a digital camera, a backpack, a loaded SKS-style rifle with a scope and a plastic bag containing food.

The arrest came two months after Trump was shot and wounded in the ear in an assassination attempt during a campaign rally in Pennsylvania. The Secret Service has acknowledged failings leading up to that shooting but has said that security worked as it should have to thwart a potential attack in Florida.

The initial charges Routh faced in a criminal complaint accused him of illegally possessing his gun in spite of multiple felony convictions and with possessing a firearm with an obliterated serial number. It is common for prosecutors to bring preliminary and easily provable charges upon an arrest and then add more serious offenses later as the investigation develops.

The FBI had said at the outset that it was investigating the episode as an apparent assassination attempt, but the absence of an immediate charge to that effect opened the door for Florida's Republican Gov. Ron DeSantis to announce his own state-level investigation that he said could produce more serious charges.

Trump, seeking to cast doubt on the legitimacy of the investigation and the Justice Department more broadly, complained Monday — before the attempted assassination charge was brought — that federal prosecutors were “mishandling and downplaying” the case by bringing charges that were a “slap on the wrist.”

Asked Tuesday at an unrelated press conference about Trump’s criticism, Attorney General Merrick Garland said the Justice Department “would spare no resources to ensure accountability” in the case.

“All of our top priority should be ensuring that accountability occurs in this case and that those who run for office and their families are safe and protected,” Garland said.

The Justice Department also said Monday that authorities who searched Routh's car found six cellphones, including one that showed a Google search of how to travel from Palm Beach County to Mexico.

A notebook found in his car was filled with criticism of the Russian and Chinese governments and notes about how to join the war on behalf of Ukraine.

In addition, prosecutors have cited a book authored by Routh last year in which he lambasted Trump’s approach to foreign policy, including in Ukraine. In the book, he wrote that Iran was “free to assassinate Trump” for having left the nuclear deal.

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Associated Press writers Alanna Durkin Richer and Curt Anderson contributed to this report.