A Coast Guard lieutenant accused of planning a domestic terrorist attack illegally possessed silencers among the arsenal of weapons prosecutors contend he stockpiled for his plot, according to new court filings.

A federal grand jury on Wednesday indicted Christopher P. Hasson, 49, of Maryland, adding two charges related to the unlawful possession of silencers to the drug and weapons counts he has faced since his Feb. 15 arrest.

Two silencers Hasson had in his possession did not have serial numbers and had not been registered as required by law, the U.S. attorney’s office in Maryland said in announcing Hasson’s indictment. The indictment, which does not include any terrorism-related counts, did not indicate why the silencers lacked serial numbers.

Hasson was taken into custody at work this month after a computer program the Coast Guard uses to search for insider threats flagged suspicious activity connected to him, federal authorities said. After executing a search warrant at his Silver Spring home and office, law enforcement uncovered a cache of weapons in the basement apartment Hasson lived in as well as a spreadsheet of “traitors” and politicians and media personalities he planned to attack, prosecutors said.

Prosecutors say Hasson used his government computer to plot an assault, studying the writings of mass shooters and bombers and conducting Internet searches on where to find politicians in the D.C. area.

Hasson’s federal public defender, Julie Stelzig, argued at his detention hearing that the government’s accusations were “inflammatory” and that there was no indication he planned to carry out an attack. It is not a crime to have negative thoughts, Stelzig added.

In the same alleged plot, Hasson had been charged earlier with possession of firearms and ammunition by an unlawful user of a controlled substance and unlawful possession of tramadol, a painkiller.

Last week, a federal magistrate judge ordered Hasson held so prosecutors could consider additional charges. Hasson’s next court hearing has not yet been scheduled.

Prosecutors said Hasson could face up to 31 years in prison for the three weapons charges and tramadol possession if he is convicted.

The Office of the Federal Public Defender declined to comment on Wednesday’s indictment.

Hasson has been in the Coast Guard for more than two decades and previously served in the Marine Corps and Army National Guard. His secret security clearance has been suspended, Coast Guard officials said.

In some of the writings found in his email, Hasson described himself as a “long time White Nationalist” and contemplated ways to incite violence and turmoil, according to court documents.

“I can’t just strike to wound I must find a way to deliver a blow that cannot be shaken off,” court documents say Hasson wrote in a draft email found in the “deletions” subfolder of his computer.