Updated

The Justice Department released a chilling letter written by would-be Trump assassin Ryan Wesley Routh on Monday.

The DOJ obtained the letter from a witness who says they received it inside a box delivered to them by Routh several months prior to the assassination attempt. Authorities say the witness opened the box only after hearing Routh was suspected in the attack.

The box contained several handwritten letters as well as ammunition, among other things. One of the letters, addressed "Dear World," admitted to an assassination attempt on Trump. He also offered money to anyone willing to finish the job.

WATCH ON FOX NATION: THE ATTEMPTED ASSASSINATIONS OF DONALD TRUMP

Ryan W. Routh stands handcuffed after his arrest

Ryan W. Routh, suspected of attempting to assassinate Republican presidential nominee and former U.S. President Donald Trump at his West Palm Beach golf course, stands handcuffed after his arrest during a traffic stop near Palm City, Florida, U.S., September 15, 2024.   (Martin County Sheriff's Office/Handout via REUTERS)

In the letter, Routh criticized Trump as unfit for office.

The detention memo revealed that Routh traveled from Greensboro, North Carolina, to West Palm Beach, Florida, on Aug. 14, a month before the Sept. 15 golf course incident. One of Routh's cell phones pinged cell towers near Trump's golf course and his Mar-a-Lago residence "on multiple days and times" from Aug. 18 to Sept. 15, the detention memo alleged.

Investigators say they also found a book Routh had authored in 2023, titled "Ukraine’s Unwinnable War: The Fatal Flaw of Democracy, World Abandonment and the Global Citizen-Taiwan, Afghanistan, North Korea, WWIII and the End of Humanity."

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The rifle Ryan Wesley Routh had during his alleged assassination attempt against former President Donald Trump.

The rifle Ryan Wesley Routh had during his alleged assassination attempt against former President Donald Trump.

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The book also discusses a Trump assassination, this time encouraging Iran to carry it out.

"In the book, ROUTH stated that he 'must take part of the blame for the [person] that we elected for our next president that ended up being brainless, but I am man enough to say that I misjudged and made a terrible mistake and Iran, I apologize. You are free to assassinate Trump as well as me for that error in judgment and the dismantling of the deal," DOJ documents say.

Routh has been charged federally with possessing a gun with a scratched-out number and with possessing a gun illegally as a felon, though more serious charges are likely pending. The weapon had a round in the chamber and was loaded with a total of 11 rounds, the DOJ said Monday.

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rifle aimed through fence with two bangs hanging nearby

Ryan Routh camped out on the Trump International Golf Course West Palm Beach with an SKS-style rifle, a backpack, and a shopping bag. The two bags both contained plates capable of stopping small arms fire, preliminary ballistics testing showed. (Department of Justice)

He is appearing before a federal judge today for a detention hearing. 

Routh had searched how to travel from Palm Beach County to Mexico on one of his six cell phones, the DOJ alleged.

The detention memo also provided a fresh detail on the witness who saw Routh flee the sniper's nest. The witness made eye contact with the suspect before Routh jumped into a Nissan Xterra and sped away. The witness is credited with photographing the vehicle and reporting it to law enforcement.

Routh will likely face additional charges in the coming days, which could include aggravated assault for allegedly pointing the rifle at a Secret Service agent and making threats against a former president, State Attorney Dave Aronberg previously told Fox News Digital.

Florida Gov. Ron DeSantis said in a press conference Tuesday that Florida will pursue more charges against Routh and that his offense should merit life in prison.  

Fox News' Mollie Markowitz contributed to this report