The man charged in connection with an apparent assassination attempt against Donald Trump in Florida this month dropped off at a home a box with a letter that declared, "This was an assassination attempt," a court document revealed Monday.
The note was made public in a U.S. District Court filing asking that Ryan Wesley Routh, 58, be held in pre-trial detention. Later on Monday, a judge ordered he would remain in jail pending trial.
Law enforcement was contacted Sept. 18 by a civilian who said that Routh had dropped off a box at his residence several months earlier, the filing said. The witness opened the box after learning of the Sept. 15 incident at Trump International Golf Club in West Palm Beach, Florida.
The box contained ammunition, four phones and letters.
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One handwritten letter addressed to “The World” said: “This was an assassination attempt on Donald Trump but I failed you.”
The letter said in part: “He ended relations with Iran like a child and now the Middle East has unraveled.”
Routh was arrested Sept. 15 after a Secret Service agent moving ahead of the former president as he was golfing at Trump International Golf Club spotted “the partially obscured face of a man” in the brush along the fence line and the barrel of a rifle “aimed directly at him.” The agent fired at the man, who fled. He was spotted by a witness and was soon after arrested on Interstate 95.
Routh has since been charged with possession of a firearm by a convicted felon and possession of a firearm with an obliterated serial number.
The FBI searched Routh's Nissan Xterra and found six cellphones — one of which contained a Google search of how to travel from Palm Beach County to Mexico.
Cell site records from two of the phones indicated Routh had traveled from Greensboro, North Carolina, to West Palm Beach on Aug. 14.
Further, on “multiple days and times from Aug. 18, 2024, to Sept. 15, 2024, Routh’s cellphone accessed cell towers located near Trump International and the former president’s residence at Mar-a-Lago,” the filing said.
Also found in the vehicle were 12 pairs of gloves, a Hawaii driver’s license in Routh’s name, passport and documents. One of the documents was a handwritten list of dates in August, September and October and venues where Trump had appeared or was expected to.
Agents also found a notebook with “dozens of pages” filled with names and phone numbers about Ukraine, discussions on how to join the fight on behalf of Ukraine and notes criticizing the Chinese and Russian governments.
The filing said law enforcement learned that the license plate on the Nissan Xterra was not registered to the vehicle, and two additional license plates were found in the car.
A search of the area where Routh had been hiding near the golf course led to the discovery of a rifle with a scope attached and obliterated serial number, an extended magazine, a backpack and a reusable shopping bag that contained plates “capable of stopping small arms fire.”
On the rifle, investigators found a latent fingerprint on a piece of tape attached to the firearm that preliminarily matched Routh.
NBC News observed heavy police presence and tape near a row of palm trees and bushes lining the golf course on Summit Boulevard after the apparent assassination attempt last week.
On Thursday, after law enforcement re-opened the road to the public, NBC News identified an opening in the bushes behind the palm trees, which is easily accessible from the public sidewalk. The gap had a view of the golf course and was large enough for someone to occupy.
Routh appeared in Florida court for nearly three hours Monday, where prosecutors alleged he went to Trump International Golf Club with the goal of assassinating Trump.
“Any established ties to southern district of Florida is for one reason only and that was to kill former President Trump,” the prosecutor said to the judge.
His defense attorney said Routh’s sister is a licensed attorney in North Carolina and was willing to house him if he was released on bail. Ultimately, U.S. Magistrate Judge Ryon M. McCabe ruled Routh would be held pending his trial.
Routh appeared emotionless throughout the hearing, wearing a blue jumpsuit and shackled at his hands and feet. He appeared to nod his head when the defense questioned an FBI special agent about Routh's social media posts about fighting for Ukraine.
This story first appeared on NBCNews.com. More from NBC News: