A Virginia man was arrested this month with what federal prosecutors described in court papers on Monday as the largest cache of “finished explosive devices” ever found in the F.B.I.’s history. The man, Brad Spafford, was taken into custody at a farm outside Norfolk on Dec. 17 on the basis of a single-count criminal complaint accusing him of illegally possessing an unregistered short-barrel rifle. When investigators searched his 20-acre property, in Isle of Wight County, they found in a detached garage more than 150 explosive devices — mostly pipe bombs, some of them labeled “lethal,” prosecutors said.

They found more pipe bombs in a bedroom inside Mr. Spafford’s house, loosely stuffed in a backpack that bore a patch shaped like a hand grenade and a logo reading “#NoLivesMatter,” prosecutors said. No Lives Matter is a nihilistic, far-right ideology that largely exists on encrypted online messaging apps like Telegram. The movement’s adherents promote “targeted attacks, mass killings and criminal activity” and have “historically encouraged members to engage in self-harm and animal abuse,” according to a threat assessment released in August by the New Jersey Office of Homeland Security and Preparedness.

Prosecutors in Federal District Court in Norfolk filed the court papers describing Mr. Spafford’s explosives in an effort to keep him in custody as his case moves toward trial.

According to the court papers, which were reported earlier by the website Court Watch, the investigation into Mr. Spafford began last year, after a neighbor reached out to the authorities. Mr. Spafford had lost three fingers on his right hand while working with a homemade explosive device, the neighbor said, and he was stockpiling weapons and homemade ammunition.

The neighbor reported that Mr. Spafford had told him that he and his friends were “preparing for something” that he “would not be able to do alone,” the court papers said.

The neighbor also told investigators that Mr. Spafford sometimes used photographs of President Biden for target practice at a local shooting range and believed that “political assassinations should be brought back.” After the attempt on President-elect Donald J. Trump’s life in Pennsylvania in July, the papers said, Mr. Spafford told his neighbor that he “hoped the shooter doesn’t miss Kamala,” an apparent reference to Vice President Kamala Harris.

Mr. Spafford moved to his farm this fall, and the neighbor went to visit him there in October wearing a secret recording device, the papers said. Mr. Spafford told the neighbor that he had various types of explosives at the property and discussed fortifying it with “a 360-degree turret” in which he planned to mount a 50-caliber rifle, according to the papers.

No Lives Matter is an offshoot of the broader “accelerationist” movement, which seeks to accelerate radical social change through sabotage and violence. Some scholars of far-right extremism believe it takes its name from a song entitled “No Lives Matter,” by the pro-Trump Canadian rapper Tom MacDonald.