A man accused of lurking outside Donald Trump’s south Florida golf course on 15 September with a gun – and allegedly writing about his desire to kill him – was charged on Tuesday with attempting to kill the Republican presidential candidate.

Ryan Wesley Routh, 58, was indicted on five counts in south Florida federal court: attempted assassination of a major political candidate, possessing a firearm in furtherance of a crime of violence, assaulting a federal officer, felon in possession of a firearm and ammunition, and possession of a firearm with an obliterated serial number. He was first charged with federal firearms crimes after his arrest.

“Violence targeting public officials endangers everything our country stands for, and the Department of Justice will use every available tool to hold Ryan Routh accountable for the attempted assassination of former President Trump charged in the indictment,” the US attorney general Merrick Garland said in a statement.

“The justice department will not tolerate violence that strikes at the heart of our democracy, and we will find and hold accountable those who perpetrate it. This must stop.”

Prosecutors have laid out what they allege is evidence of a murder plot. Routh left behind a missive, addressed “Dear World”, in which he described his apparent intent to kill Trump; the note was put in a box, which had been left at the home of a person who authorities have not identified, officials said.

The recipient did not open this box – in which there was also allegedly ammunition and a metal pipe – until after Routh’s arrest. This person contacted authorities.

“This was an assassination attempt on Donald Trump but I failed you. I tried my best and gave it all the gumption I could muster. It is up to you now to finish the job; and I will offer $150,000 to whomever can complete the job,” the note read, which prosecutors disclosed in a memorandum arguing for Routh’s detention.

Routh’s note appeared to suggest Trump’s foreign policy decisions played into the motive behind his alleged assassination attempt, as it said that the ex-president “ended relations with Iran, like a child, and now the Middle East has unraveled”.

Authorities believe Routh staked out the golf course for a month before the alleged attempt on Trump’s life; on that day, he hid outside the fence near the sixth hole of the grounds. A US Secret Service agent on site, who was monitoring a hole ahead of Trump’s party, said he saw “the barrel of a rifle aimed directly at him”.

As the agent started backing up, he saw the rifle barrel move and fired at Routh, prosecutors said. Routh ran across the road from the golf course, and took off in his Nissan SUV; he was subsequently caught traveling north on I-95.

The prosecution said Routh planned to use a semi-automatic rifle, fitted with a scope, to open fire on Trump. There was a bullet in the rifle’s chamber, and 11 more in the gun, which Routh left behind when he tried to escape, prosecutors said.

“At approximately 1.30pm, the agent spotted the partially obscured face of a man in the brush along the fence line,” prosecutors’ detention memo stated, which as “directly in line with the sixth hole”.

“The agent then observed a long black object protruding through the fence and realized the object was the barrel of a rifle aimed directly at him,” the filing said, further noting: “The agent jumped out of the golf cart, drew his weapon, and began backing away. The agent saw the rifle barrel move, and the agent fired at Routh.

“The agent took cover behind a tree and reloaded his weapon, then looked up and saw that Routh was gone. The agent called out over his radio that shots had been fired by the agent and that there was a subject with a rifle.”

When authorities searched Routh’s SUV upon his arrest, they claimed to have found “a handwritten list of dates in August, September and October, and venues where the former president had appeared or was expected to be present”, and six mobile phones. On one of these cellphones, there had been a Google search for how to travel from Palm Beach to Mexico City, prosecutors said.

Before the alleged assassination attempt, Routh had had repeated run-ins with police. Routh was convicted in 2002 of illegally possessing what a report described a “fully automatic machine gun”. The Greensboro News & Record said Routh had barricaded himself at his roofing business in a three-hour standoff that turned into a car chase before his eventual surrender.

Ruth also has a second felony conviction for multiple counts of possession of stolen goods, prosecutors said.