A United States Capitol Police officer died on Thursday night from injuries sustained “while physically engaging” with pro-Trump rioters who descended on the U.S. Capitol the day before, the fifth fatality linked to the chaos that engulfed the nation’s capital on Wednesday, according to the authorities.
The officer, Brian D. Sicknick, was only the fourth member of the force to be killed in the line of duty since its founding two centuries ago. After the bedlam of Wednesday’s siege and the recriminations that filled the airwaves the next day, a silence descended over the Capitol grounds late Thursday as hundreds of law enforcement officers from scores of agencies lined the streets to pay tribute to their fallen comrade.
But the loss of life also underscored the failure of law enforcement agencies to prevent the siege of the Capitol. And with leaders of both political parties calling for investigations, it appeared likely to lead to calls for profound changes to the Capitol Police.
The circumstances surrounding Mr. Sicknick’s death were not immediately clear, and the Capitol Police said only that he had “passed away due to injuries sustained while on duty.” At some point in the chaos — with the mob rampaging through the halls of Congress while lawmakers were forced to hide under their desks — he was struck with a fire extinguisher, according to two law enforcement officials.
“He returned to his division office and collapsed,” the Capitol Police said in the statement. “He was taken to a local hospital, where he succumbed to his injuries.”
Mr. Sicknick, who joined the force in 2008, died at about 9:30 p.m. on Thursday, the Capitol Police said in a statement. The Washington police department’s homicide branch is one of several law enforcement agencies involved in an investigation into his death and the overall circumstances of the violence at the Capitol.
The officer’s death brings the fatalities from Wednesday’s mayhem to five. One participant in the pro-Trump rampage, Ashli Babbitt, was fatally shot by a Capitol Police officer inside the building as she climbed through a broken window leading to the Speaker’s Lobby. Three other people died after experiencing what were believed to be medical emergencies in the area around the Capitol, the police said.
It was unclear where Mr. Sicknick’s encounter with the rioters took place, but photos and a video posted by a local reporter during the night of chaos showed a man spraying a fire extinguisher outside the Senate chamber, with a small number of police officers overlooking the area on a nearby stairway.
Lawmakers in both chambers and from both parties vowed to find out how those responsible for Capitol security had allowed a violent mob to infiltrate the building. House Democrats announced a “robust” investigation into the law enforcement breakdown.
Three of Congress’s top security officials — Capitol Police Chief Steven A. Sund, House Sergeant at Arms Paul D. Irving and Senate Sergeant at Arms Michael C. Stenger — announced their resignations on Thursday.
The sergeants-at-arms are responsible for security in the chambers and related office buildings, while Mr. Sund oversaw roughly 2,000 Capitol Police personnel — a force larger than that of many small cities.
Early Friday, Representative Tim Ryan of Ohio, a Democrat who runs the House Appropriations subcommittee that oversees the Capitol Police’s budget, expressed sorrow in a Twitter post over Mr. Sicknick’s death.
“This tragic loss is a reminder of the bravery of the law enforcement who protect us every day,” Mr. Ryan wrote.
Representative Rosa DeLauro, a Connecticut Democrat who is chairwoman of the House Appropriations Committee, which opened a review into the law enforcement response to the Capitol riot, said her “heart breaks over the senseless death.”
“To honor his memory, we must ensure that the mob who attacked the People’s House and those who instigated them are held accountable,” she said on Twitter.
Hundreds of police officers and emergency response personnel lined the streets by the Capitol for a moment of silence to honor Mr. Sicknick on Thursday night. They stood in lines on Constitution Avenue and 3rd Street, saluting in silence as a police motorcade for Mr. Sicknick passed through the city, according to videos from local reporters at the scene.
The police force said in its own statement that “the entire U.S.C.P. department expresses its deepest sympathies to Officer Sicknick’s family and friends on their loss, and mourns the loss of a friend and colleague.”
Officials have said that about 50 police officers were injured as the mob swarmed barricades, threw objects, battered doors, smashed windows and overwhelmed some of the officers who tried to resist the advancing crowd.
The Capitol Police reported 14 arrests during the incursion, including two people accused of assaulting a police officer. The local police arrested dozens of others, mostly in connection with unlawful entry and violations of the city’s Wednesday night curfew.
The Capitol Police force is charged solely with protecting the Capitol and surrounding grounds.
Over the course of two centuries, the force has evolved, its mission shifting and growing with the nature of the threats to the institution.
An event that had one of the most profound impacts on the force played out on March 1, 1954, when Puerto Rican nationalists opened fire from the visitor’s gallery on lawmakers below, wounding five. Shortly afterward, the police were issued weapons for the first time.
Exactly 17 years later, on March 1, 1971, an explosion ripped through a ground-floor restroom in the Senate wing. The Weather Underground, a militant left-wing group that carried out a series of bombings in the late 1960s and 1970s, took responsibility. The incident led to the requirement of checking all visitors for weapons and explosives.
The first recorded death of a member of the force was in 1984, when Sgt. Christopher Eney, 37, was killed during a training exercise.
The last time a Capitol Police officer was killed in the line of duty was in the summer of 1998, when Officer Jacob J. Chestnut and Detective John Gibson were fatally shot by Russell Eugene Weston Jr., a man tormented by visions of an oppressive federal government.
Mr. Weston, who was shot and injured in the incident, blasted his way into the nation’s centerpiece of law and order. It all played out in a matter of minutes, reaching its bloody conclusion when he reached the majority whip’s ground-floor office complex.
A fourth person, Angela Dickerson, 24, a tourist, was injured but recovered.
President Bill Clinton called the gunfight just inside the East Front entrance to the nation’s lawmaking forum “a moment of savagery at the front door of American civilization.”
Lawmakers from both parties said at the time that they hoped the bloodshed would allow for a moment reflection, when partisan divisions could start to be healed.
Two decades later, the fourth Capitol Police officer in history was killed.
Emily Cochrane and Katie Benner contributed reporting.