The man who authorities say sat with a rifle in the trees where Donald Trump was golfing earlier this month in West Palm Beach, Florida, previously wrote a letter stating “this was an assassination attempt on Donald Trump,” according to a new filing by federal prosecutors.

A witness told investigators that Ryan Wesley Routh had dropped off a box at his home months before, which “contained ammunition, a metal pipe, miscellaneous building materials, tools, four phones, and various letters.” After learning of the apparent assassination attempt, the witness opened the box, according to the filing.

One letter, addressed to “The World” said: “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.”

Trump “ended relations with Iran like a child and now the Middle East has unraveled,” the letter says.

Routh, 58, was charged with two firearm offenses last week after allegedly fleeing the Trump International Golf Course. More serious charges could be brought in the case as the investigation continues.

He will appear in court Monday for a detention hearing.

Prosecutors say a Secret Service agent fired at Routh after spotting a rifle poking out of the tree line several holes ahead of where Trump was golfing on September 15, and that Routh was spotted by a witness running away from the scene and driving off.

The complaint against Routh says cell phone data shows he may have been lying in wait for nearly 12 hours at the golf course. He was arrested after law enforcement spotted his car driving on a nearby highway.

Had list of Trump locations; searched for how to get to Mexico

Prosecutors say Routh was in the area of Trump’s golf course and the former president’s Mar-a-Lago residence across multiple days in the month before he was arrested and had a Google search of how to travel from Florida to Mexico in one of his phones.

Routh also had a handwritten list of dates and venues where Trump has or was expected to appear in the lead-up to the 2024 presidential election.

Prosecutors wrote that Routh had traveled to West Palm Beach from North Carolina on August 14. Cell phone data shows him near Trump’s Mar-a-Lago residence and the golf course “multiple days and times” between August 18 and September 15, the day he was arrested, prosecutors say.

While searching Routh’s car, agents found six cell phones, one of which included “a Google search of how to travel from Palm Beach County to Mexico.”

“The agents also found 12 pairs of gloves; a Hawaii Driver’s License in the Defendant’s name; a passport in the Defendant’s name,” the filing says.

Routh’s recent background included a stint in Ukraine, where he unsuccessfully tried to be recruited to fight Russia, as well as time in Hawaii working in construction.

In online posts, frequently focused on US politics and global events, Routh said he voted for Trump in 2016 but that the president had become a disappointment, adding that “I will be glad when you gone.”

Routh, in a self-published book, also told the country of Iran: “You are free to assassinate Trump.”

This story has been updated with additional details.