• N.C. man surrenders in bomb threat near U.S. Capitol.

WASHINGTON — A North Carolina man who claimed to have a bomb in a pickup truck near the U.S. Capitol surrendered to law enforcement after an hourslong standoff Thursday that prompted a massive police response and the evacuations of government buildings in the area.

Authorities were investigating what led the suspect, identified as 49-yearold Floyd Ray Roseberry, to drive onto the sidewalk outside the Library of Congress, make bomb threats to officers and profess a litany of antigovernment grievances as part of a bizarre episode that he livestreamed for a Facebook audience. Police later searched the vehicle and said they did not find a bomb but did collect possible bomb-making materials.

The standoff was resolved peacefully after roughly five hours of negotiations, ending when Mr. Roseberry crawled out of the truck and was taken into police custody. But even in a city with a long history of dramatic law enforcement encounters outside federal landmarks, this episode was notable for its timing — Washington remains on edge eight months after the insurrection at the U.S. Capitol — and for the way the suspect harnessed social media to draw attention to his actions in the hours before his arrest.

Authorities who spent hours negotiating with Mr. Roseberry — he held up handwritten signs through his driver-side window — were continuing to dig into his background Thursday evening. They did not reveal any details about a motive, and no charges were immediately announced.

Investigators had been speaking with members of Mr. Roseberry’s family and learned that his mother had recently died, Capitol Police Chief J. Thomas Manger said. “There were other issues he was dealing with,” the chief said, without providing specific details.

As police continued negotiations, video surfaced of Mr. Roseberry on Facebook Live inside the truck, which was stuffed with coins and boxes. He threatened explosions, expressed hostility toward President Joe Biden, profanely warned of a “revolution,” and laid bare a series of grievances related to U.S. positions on Afghanistan, health care and the military.

Thursday’s incident began around 9:15 a.m. when a truck with no license plates drove up the sidewalk outside the library.

Kelsey Campbell, a student at the University of Wisconsin-Madison visiting Washington as part of a class trip, said she and another student encountered Mr. Roseberry around 9:20 a.m. outside the nearby Supreme Court building. Ms. Campbell said he was with his truck, which was parked next to the sidewalk, and was holding a large stack of dollar bills.

“He said, ‘Hey, call the police, tell them to evacuate this street, and I’ll give you all this money,’ ” Ms. Campbellsaid. “I said, ’No!’ and he threw the money at us and we started running.”

Ms. Campbell said she and the other student saw police officers standing nearby and told them what happened. The officers then went to confront Mr. Roseberry.