The man accused in the apparent assassination attempt of Donald Trump at a golf course in Florida left behind a note saying that he intended to kill the former president and maintained in his car a handwritten list of dates and venues where the Republican White House nominee was to appear, the justice department said on Monday.

The new allegations were included in a detention memo filed ahead of a hearing on Monday at which the justice department was expected to argue that 58-year-old Ryan Wesley Routh should remain locked up while the case is pending.

The details are meant to buttress prosecutors’ assertions that Routh had set out to kill Trump before the plot was thwarted by a Secret Service agent who spotted a rifle poking out of shrubbery on the West Palm Beach golf course where the former president was playing on 15 September.

The note, addressed “Dear World”, was placed in a box that was dropped at the home of an unidentified person who contacted law enforcement officials after last Sunday’s arrest. It appears to have been based on the premise that the assassination attempt would ultimately be unsuccessful.

The box, which also contained ammunition, a metal pipe and other items, was not opened by the person until after Routh was taken into custody. The person who received the box and contacted law enforcement was not identified in the justice department’s detention memo.

“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 said, according to prosecutors.

An attorney for Routh did not immediately respond to an email seeking comment on Monday morning.

The letter gives further indications of Routh’s alleged motivation. The former president “ended relations with Iran like a child and now the Middle East has unraveled”, the note states, apparently alluding to the Trump White House’s decision to withdraw from a nuclear agreement with Iran in 2018.

Investigators believe that Routh, a pro-Ukraine activist, had staked out the grounds of Trump’s West Palm Beach golf course for a month before his arrest, the filing said. On the day of the apparent attempt on Trump’s life, he had secreted himself outside the fence at the 6th hole of the course.

A Secret Service agent patrolling one hole ahead of Trump’s group spotted Routh and the barrel of his gun, eventually leading to his arrest.

Prosecutors say Routh positioned himself near the 6th hole with the intention of using a semiautomatic rifle equipped with a scope to shoot Trump. Routh had a round in the rifle’s chamber and 11 additional bullets in the weapon, which he left at the scene after being spotted and trying to flee.

The memo states that “at approximately 1.30pm, the agent spotted the partially obscured face of a man in the brush along the fence line … 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 memo adds: “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.”

Prosecutors submitted the note as part of a filing arguing for Routh to be detained in custody while he awaits trial on two gun charges.

During a search of Routh’s Nissan SUV after authorities caught him, the memo said, investigators also found “a handwritten list of dates in August, September and October 2024 and venues where the former president had appeared or was expected to be present”.

Agents also found six cellphones (including one that contained a Google search of how to travel from Palm Beach county to Mexico), 12 pairs of gloves, a Hawaii driver’s license in Routh’s name and a passport.

After he was arrested, Routh was charged with possessing a firearm despite a prior felony conviction prohibiting him from legally doing so as well as possession and receipt of a firearm with an obliterated serial number.

The memo alleges that, in the area of the tree line where Routh was hiding, agents found a digital camera, a backpack, a loaded SKS-style rifle with a scope and a black plastic bag containing food. The serial number on the rifle was obliterated, which is against federal law.

Deputies with the nearby Martin county sheriff’s office later arrested Routh in coordination with the Palm Beach county sheriff’s office as he headed north.

Monday’s memo noted how Routh’s arrest was not his only brush with the law. The document made reference to a 2002 conviction of illegally possessing what a media report referred to at the time as a “fully automatic machine gun”. According to the Greensboro News & Record, in that case Routh barricaded himself at his roofing company during a three-hour standoff before he led police on a car chase and ultimately surrendered.

A second felony conviction mentioned in Monday’s memo dated back to 2010 and was for multiple counts of possession of stolen goods.

The Associated Press contributed reporting