A federal judge on Monday ordered Ryan Routh, the man accused in connection with an assassination attempt against former President Trump earlier this month, held in custody. 

Magistrate Judge Ryon McCabe granted the government’s request to detain Ryan Routh pending the resolution of these charges during a court hearing in Florida. 

Prior to the hearing, the Justice Department asked the United States District Court for the Southern District of Florida to keep Routh in pretrial detention. McCabe said federal prosecutors met its burden and the weight of the evidence was strong.

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. Federal prosecutors also told the judge that the government intends to ask a grand jury to indict Routh on the much more serious charge of the attempted assassination of Trump.

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A general view of the fenced area near the sixth hole of Trump International Golf Club in West Palm Beach, Florida, on Wednesday, Sept. 18. The area is where Ryan Routh is reported to have lay in wait for former President Trump on Sunday. (Peter Burke/Fox News Digital/Palm Beach County Sheriff’s Office)

In addition, prosecutors said they have an audio recording of a recent jailhouse phone call from Routh to a female friend. During the call, Routh said he was "sorry," while the friend said she was still "processing" the worst possible thing he could have done. 

Prosecutors said Routh then apologized a second time. 

Routh will likely face additional charges in the coming days, which could include aggravated assault for allegedly pointing the rifle at a U.S. 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 last Tuesday that Florida will pursue more charges against Routh and that his offense should merit life in prison.   

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Ryan Routh camped out near the Trump International Golf Course in 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, a preliminary ballistics testing showed.

On Monday, the Justice Department also released a chilling letter written by Routh. 

The Justice Department 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," discussed the assassination attempt. 

FBI investigators carry a box of evidence from the perimeter of Trump International Golf Club in West Palm Beach, Florida on Monday, Sept. 16, 2024. Ryan Routh was arrested earlier this week after allegedly attempting to assassinate former President Donald Trump while hiding in the bushes along the golf course. (Mega for Fox News Digital)

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Routh had written in the letter that he had failed and that he would give $150,000 to anyone who could finish the job. 

McCabe said it appeared Routh was stalking Trump for 30 days and had a passport with him when he was caught along with a phone, which had a search history of how to travel from Palm Beach to Florida.

Fox News’ Anders Hagstrom, Jake Gibson and David Spunt contributed to this report.