David N. Dempsey came to the Jan. 6, 2021, attack on the U.S. Capitol well prepared and well experienced in committing violence at political rallies. Dempsey wore a bullet-proof tactical vest, a black helmet, a gaiter to obscure most of his face, and he brought a spare gaiter and shirt that he changed into during the riot.

Before climbing up over rioters on the steps of the Capitol, he gave an interview in front of the gallows constructed nearby and rattled off the names of prominent Democrats he hated. “They don’t need a jail cell,” Dempsey said. “They need to hang from these.”

Dempsey then repeatedly attacked police officers in the lower West Terrace tunnel for more than an hour, throwing poles and deploying bear spray at the line of officers protecting the Capitol. He then sprayed bear spray directly inside the mask of one officer, who testified that he thought he might die, and used a crutch to smash one officer’s head, giving him a concussion.

Senior U.S. District Judge Royce C. Lamberth sentenced Dempsey, 37, to 20 years in prison Friday, the second-longest sentence of the approximately 950 defendants sentenced so far. Only Enrique Tarrio, the leader of the Proud Boys who was convicted of seditious conspiracy, received a longer sentence of 22 years.

“Your conduct on January 6 was especially egregious,” Lamberth told Dempsey. “You didn’t make a split-second decision to use violence. You did not get carried away in the moment. You have a long and well-documented history of inflicting violence on political opponents.”

Dempsey pleaded guilty in January of this year to two counts of assaulting police with dangerous or deadly weapons in the Capitol attack. His family started an online fundraiser for him, which has raised more than $20,000, saying that “he is being politically silenced for his beliefs in the Constitution.”

The judge also weighed Dempsey’s lengthy criminal history in California for burglary, drug dealing, evading police and “assault with a caustic chemical,” for spraying bear spray at anti-Trump protesters in 2020, one of multiple attacks he allegedly launched at political rallies.

Nearly 1,500 people have been charged in the Capitol riot, and more than a third of those were charged with assaulting the police. The average sentence for assaulting police has been slightly less than four years, according to a Washington Post database.

But “Dempsey was one of the most violent rioters, during one of the most violent stretches of time,” prosecutors argued in their sentencing memo, “at the scene of the most violent confrontations at the Capitol on January 6.” That was the West Terrace tunnel, where rioters used sheer numbers to push officers from U.S. Capitol and D.C. police back toward an internal door, hurling items, spraying chemicals and cursing the officers.

Prosecutors said Dempsey flew from his home in Van Nuys, Calif., to Detroit on Jan. 4, then drove with friends to Washington on Jan. 5. Shortly before 4 p.m. on Jan. 6, as rioters continued to swarm the Capitol, Dempsey was captured on video climbing atop the shoulders and backs of others to reach the front line of the skirmish, where he announced his presence by throwing a short pole at an officer and cursing them.

Dempsey grabbed whatever was nearby and threw it at police, prosecutors said, including a riot shield and a flagpole, swung a pole into some officers, then unleashed two bursts of spray into the line of officers. Then as fellow rioter Kyle Fitzsimons of Maine yanked at the gas mask of D.C. police Sgt. Phuson Nguyen, Dempsey fired some spray into Nguyen’s face before Fitzsimons snapped the mask shut, trapping the chemicals inside.

“I thought that’s, you know, where I’m going to die,” Nguyen testified in 2022 at Fitzsimons’s trial. “And in my head, I was thinking about my family at that point before anything else.”

Fitzsimons then got smashed in the top of his head by another rioter swinging a crutch. It’s not clear whether Dempsey was the one who inflicted that wound, but surveillance video later captured Dempsey swinging a crutch at officers at least nine times, striking D.C. police Sgt. Jason Mastony in the head and arm.

Prosecutors said Mastony declined to provide a victim impact statement in other cases but did so in Dempsey’s case because “Dempsey is one of the most violent rioters I encountered on Jan. 6.” Mastony said Dempsey’s crutch struck his head “with such force that it cracked the plastic face shield of my gas mask. I collapsed and caught myself against the wall as my ears rang.” Mastony told investigators he believed he suffered a concussion.

Dempsey remained in the tunnel, surveillance video showed, continuing to swing the crutch and poles at officers before retreating at about 4:42 p.m. Then, prosecutors said, he changed his gaiter and shirt, removed his helmet and put on a hat, and returned to the fray, continuing to swing and throw things at police. He was still fighting and throwing things past 5 p.m., prosecutors said.

Dempsey was first identified by a group of online sleuths who used open-source video and photos to supply suspect names to the FBI, as detailed in the book “Sedition Hunters” by NBC News reporter Ryan Reilly. The sleuths, who initially dubbed Dempsey “FlagGaiterCopHater,” even noticed Dempsey’s change of outfits, but he continued to wear the same Converse high-top sneakers and camouflage pants throughout.

Dempsey appears to wear the same or similarConverse sneakers in Santa Monica, Calif., in 2019, video shows, when he was arrested after spraying anti-Donald Trump protesters with bear spray. He was convicted of that assault in 2021 and received a two-year suspended sentence. Dempsey was also photographed assaulting anti-Trump protesters with a metal bat and a skateboard, twice, at three rallies in 2019 and 2020 but wasn’t charged, prosecutors said.

Dempsey was arrested on multiple felony counts in August 2021 and has been held in jail since. His lawyers did not file any motions seeking his release in the intervening three years, an indication that they expected him to face a lengthy prison sentence.

Dempsey’s criminal record was so long he was classified as “criminal history category 6” for purposes of calculating his sentencing guidelines, the highest category. Someone with no criminal record would have qualified for a sentence of 10 to 12 years. Dempsey’s guidelines called for a sentence of 17 to nearly 22 years, and prosecutors asked Lamberth to give Dempsey the high end of that range.

In front of a packed courtroom with a number of officers who were at the Capitol on Jan. 6, Dempsey apologized to the police and the community. “You were doing your duties and I responded with anger and violence,” Dempsey said. “To the officers and their families, I really am sorry about everything that has transpired and I hope you find it in your hearts to forgive me.”

Lamberth noted that on Jan. 6, Dempsey “spoke at length about the need to lynch various public officials.” The judge said Dempsey “used every instrument at your disposal…to inflict the maximum harm on the members of the ‘thin blue line’ protecting members of Congress and the Capitol.” The judge declined to give the 22-year sentence sought by prosecutors, but imposed the longest sentence yet on a defendant convicted of assaulting the police at the Capitol.