Sentencing has begun for the Bethesda, Md., man found with bomb-making materials in his room.
Collin McKenzie-Gude, 20, pleaded guilty in September to possession of an unregistered destructive device. He faces up to 10 years in prison.
Officials said the sentencing hearing could take several days.
Police searched his home two years ago and found several weapons, including an AK-47, two shotguns and two smoke grenades.
McKenzie-Gude's attorney has said his client was fascinated with explosives but never intended to hurt anyone.
The sentencing was supposed to happen last week, but the judge postponed it to allow a key government witness to testify as the defense had asked.