The man accused of attempting to assassinate Donald Trump at a golf course in Florida left behind a note saying that he intended to kill the former president, American authorities said.

Ryan Wesley Routh also kept handwritten list of dates and venues where Mr Trump was to appear in his car, the US justice department added.

The new allegations were included in a detention memo filed ahead of a hearing at which the justice department is expected to argue that 58-year-old Routh should remain locked up as the case moves forward.

The details are meant to buttress prosecutors’ assertions that Routh had set out to kill Mr 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 Mr Trump was playing.

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 be ultimately 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.

According to prosecutors, the note read: “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.”

Authorities who searched Routh’s car found six mobile phones, including one that showed a Google search on how to travel from Palm Beach County to Mexico.

They also found a list with dates in August, September and October and venues where Mr Trump had appeared or was scheduled to appear, according to prosecutors.

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.

Phone records indicate Routh travelled to West Palm Beach from Greensboro in mid-August, and that he was near Mr Trump’s golf club and the former president’s Mar-a-Lago residence “on multiple days and times” between August 18 and the day of the apparent attempted assassination.