WEST PALM BEACH, Fla. — A federal prosecutor said Monday that the government will seek to have the gunman accused of bringing a rifle to Donald Trump’s golf course charged with attempting to assassinate the former president, a charge that could carry a penalty of up to life in prison.

Assistant U.S. attorney Mark Dispoto said Ryan Routh had been in Florida for at least a month before a Secret Service agent spotted him at Trump’s golf club in West Palm Beach. The prosecutor said Routh hid in waiting in what he likened to a “sniper’s nest.” And the gunman wrote a note stating, “This was an assassination attempt,” according to a court filing.

“He was there for one reason and one reason only,” Dispoto said. “He was there to kill the former president of the United States.”

Routh is being held on federal gun charges. Magistrate Judge Ryon M. McCabe said Monday that he would remain detained, rejecting an attempt by Routh’s defense to have him released on bond. Charging Routh with attempting to kill Trump initially was complicated by the fact that he did not fire a shot. But the evidence submitted by prosecutors Monday makes a stronger argument that his intention was to kill the former president.

Dispoto said prosecutors would “ask a grand jury to consider that this was a definite attempt to assassinate former President Trump.”

The former contractor’s defense offered a different interpretation of what transpired Sept. 15. Routh’s lawyer characterized the events as a publicity stunt, suggesting that the amateur setup should not be considered a serious attempt to kill the Republican presidential nominee.

The incident was the second time in about as many months that someone tried to kill Trump, and the evidence disclosed Monday will probably raise more questions about security for the former president. Monday’s court filing says two cellphones discovered when Routh was arrested show he had been near the golf course and Trump’s Mar-a-Lago property multiple times between Aug. 18 and Sept. 15. That suggests he may have been scoping out Trump’s whereabouts and the landscape for up to a month before the alleged attempt on the former president’s life.

The cellphone data also indicated that Routh traveled from North Carolina to West Palm Beach on Aug. 14, according to the court filing. Authorities said the cell data shows that the suspect Googled on one of the phones how to travel from Palm Beach County to Mexico.

In a court filing submitted before the hearing, prosecutors said a civilian contacted law enforcement after the golf course incident to tell them that Routh had given them a box several months earlier. The civilian, who was not identified in the filing, opened the box after learning of Routh’s arrest, the filing said. Inside, the person found multiple letters.

“Dear World,” one of the handwritten letters said, according to a copy of the letter shared in the filing. “This was an assassination attempt on Donald Trump but I am so sorry I failed you. I tried my best and gave it all the gumption I could muster.” Routh, who investigators say has little money, went on to offer a six-figure reward for someone to “finish the job.”

Trump on Monday released a statement criticizing the initial charges brought against Routh, calling them “a slap on the wrist.” In his statement, Trump reiterated a host of his familiar grievances against the Justice Department and the FBI. Trump has long complained about those agencies and other government investigations and officials that have scrutinized his conduct.

The former president said that the Justice Department and FBI had “a Conflict of Interest” due to the investigations and cases brought against him, suggesting that Florida be allowed to investigate the case instead of federal agencies.

Florida Gov. Ron DeSantis, a Republican who unsuccessfully challenged Trump for their party’s presidential nomination, announced last week that he was launching a state investigation into the case. Trump’s statement Monday echoed some of DeSantis’s rhetoric, in which the governor suggested it was improper for agencies prosecuting Trump to also investigate the golf course incident.

The Sept. 15 incident has heightened concerns about how well Trump is being protected as he goes about his day and campaigns for president. His security was bolstered after an assassination attempt in July at a rally in Pennsylvania, but authorities have long worried about his vulnerability on golf courses, especially those near public roads. The federal complaint against Routh alleges he spent nearly 12 hours in the bushes around Trump International Golf Club before a Secret Service agent spotted his rifle.

Acting Secret Service director Ronald L. Rowe Jr. is urging Congress to heavily invest in the protective agency in the aftermath of the two potential attempts on Trump’s life.

The Secret Service released a report Friday on the July 13 assassination attempt against Trump in Pennsylvania that found the agency responsible for multiple security failures that led to the attack at a campaign rally.

The internal review found that agents failed to use technology that might have detected the attacker as he flew a drone over the rally venue hours earlier. And the Secret Service, which is the lead agency in charge of security for presidents, former leaders and other top U.S. officials, never directed local police snipers to cover a nearby rooftop, even though the snipers were willing to do it.

Rowe has praised the agents for their planning and security in the West Palm Beach incident. Authorities have said a Secret Service agent moving ahead of Trump at the course fired at Routh after seeing a rifle poking out of shrubbery. Witnesses told police they saw Routh run away and flee in a Nissan SUV. One witness took a photo of the vehicle’s license plate. Routh was pulled over 45 minutes later on Interstate 95 in Martin County, about 40 miles north.

Investigators found items in the bushes they said they think Routh left behind, including a loaded SKS-style rifle with a scope, as well as food and two bags. One bag contained ceramic plates, which are often used as body armor, according to the complaint filed against him.

The gun crimes Routh is facing include possession of a firearm by a felon and possession of a firearm with an obliterated serial number. The obliterated serial number makes it harder for authorities to track the weapon and determine how it was obtained. The FBI agent who wrote the federal complaint said the type of weapon Routh had is not manufactured in Florida and that the agent suspects it was obtained from another state or abroad.

At the hearing Monday, Routh sat with his shackled hands clasped together in his lap. He occasionally took notes on a yellow legal pad or spoke to one of his two attorneys. He appeared somber compared to his court appearance a week earlier, during which he repeatedly laughed and smiled.

Routh’s defense attorneys tried to cast doubt on the prosecution’s depiction of Routh as a would-be assassin. They noted his repeated run-ins with the law, but said he’d always shown up for court dates. And they pointed out that he’d once been an Eagle Scout, and years ago was commended in a local paper for confronting and chasing a rape suspect.

Defense attorney Kristy Militello said Routh’s siblings and three children “support him even after his arrest.” She argued he should be released with a GPS monitor to his sister in North Carolina, who is an attorney and had offered to take him in.

“No shots were fired. There is no documentation that Mr. Routh touched that firearm,” Militello said. “He is an unsophisticated and untrained individual.”

Berman, Stein and Barrett reported from Washington.

previous coverage

• Ukraine has been a magnet for unstable characters like Ryan Routh
• Suspected gunman at Trump golf course has quixotic past

related stories

• Americans sour on Secret Service after Trump shooting, poll finds
• Secret Service under scrutiny after potential second attempt on Trump’s life