WASHINGTON ― A self-proclaimed neo-Nazi who lived in a rapidly gentrifying neighborhood in the nation’s capital pleaded guilty on Tuesday to a single federal gun charge and could be released from custody when he’s sentenced in September.

Jeffrey Clark, who has extensive ties to the far right, came to the attention of federal law enforcement because his relatives were concerned about his violent rhetoric in the days after his younger brother and fellow neo-Nazi died by suicide in the wake of last year’s massacre at a Pittsburgh synagogue.

Clark, who stockpiled racist gear in his room, considered the Pittsburgh shooter a “hero” and said his victims “deserved” to be killed. A federal prosecutor described Clark as “a bomb” waiting to explode. But there’s no federal law that broadly outlaws domestic terrorism, so Clark’s case presented a challenge to federal prosecutors.

In a plea deal unveiled Tuesday, Clark pleaded guilty under a law that makes it illegal to possess a firearm while using or being addicted to a controlled substance. Prosecutors dropped another count involving possession of a high-capacity magazine. Federal sentencing guidelines suggest Clark should receive 10 to 16 months in prison. Since he was arrested in November, he could potentially be released after his sentencing on Sept. 13.

Clark’s attorney, a federal public defender, argued for his release ahead of sentencing. But U.S. District Judge Timothy J. Kelly was concerned that Clark continued to pose a danger to society due to his support of violent acts, and he ordered him held.

“It’s a high bar to prove to me that there’s clear and convincing evidence that he’s not a danger,” Kelly said.

Clark was arrested in November after two members of his family alerted authorities to erratic and incendiary behavior, and his relatives told the FBI that they feared Clark ― a self-identified Nazi who attended the deadly “Unite the Right” rally in Charlottesville, Virginia, in 2017 and routinely posed for pictures in front of Nazi memorabilia ― wanted to start a race war.

But because the United States does not have a statute broadly outlawing domestic terrorism, it is difficult to prosecute right-wing extremists, including white supremacists, who may be plotting acts of violence.

Roughly 100 people the FBI has tied to domestic terrorism investigations have been arrested in the first three-quarters of the 2019 fiscal year, FBI Director Christopher Wray said Tuesday in testimony before the Senate Judiciary Committee. The majority of those cases, Wray said, “are motivated by some version of what you might call white supremacist violence.”

About half of those arrests have involved state and local charges, according to FBI officials, and others face charges that on the surface appear unrelated to terrorism.

While arguing for Clark’s release before sentencing, federal public defender David Bos pointed to the case’s “extraordinarily unique facts,” noting that the gun in question was legally registered and that possession of the controlled substance in this case ― marijuana ― is illegal under federal law but legal in Washington, where Clark was arrested.

“If the marijuana weren’t in this case, there would be no charge,” Bos said.

Bos sought to have Clark released into home incarceration until his sentencing, arguing that he would be under the supervision of the same relatives who originally reported him to authorities. He also argued that Clark would have no incentive to commit further criminal acts because he had already served the majority of the time suggested under sentencing guidelines for his crime and was likely close to release.

After his arrest, the FBI linked Clark to Robert Bowers, the white nationalist charged in the Pittsburgh killings, and court filings said Clark’s social media posts suggested that he knew “more about the attack in the Tree-of-Life synagogue, and that there was more to come.”

Federal authorities have since said there were no apparent links between Clark and Bowers, and Clark’s plea agreement indicates the government’s investigation “uncovered no evidence establishing that [Clark] had advance knowledge of the attack on the Tree of Life Synagogue in Pittsburgh, Pennsylvania, or that your client was planning an independent attack against similar targets in the District of Columbia.”

Bos argued there was “no indication that [Clark] is still ascribing” radical, alt-right beliefs.

But Kelly was unconvinced.

“I don’t know that,” he told Bos.

“There’s too much in here,” Kelly said later, holding up prosecutors’ argument against releasing Clark, “about his sympathy for folks who’ve undertaken violence ... and his support for that violence.”

Clark, like many members of white nationalist movements, was a frequent user of social media platforms ― including the Twitter alternative Gab, which is a favorite of racists and anti-Semites. His usernames included references to Dylann Roof, the man who killed nine people at a historically black church in Charleston, South Carolina, in 2015 in hopes of setting off a race war.

That history of online activity also played a role in Kelly’s decision to keep Clark incarcerated through sentencing, after a representative of D.C.’s Pretrial Services Agency ― which makes recommendations about conditional release of defendants as they face charges ― warned that it “cannot monitor Mr. Clark’s internet use” during home incarceration.

“There is no way to monitor what sites he’s visiting or who he is communicating with on the internet,” the representative told the court.