The U.S. Capitol Police officer killed in the violent riot at the Capitol Wednesday served as a staff sergeant with the New Jersey Air National Guard after graduating from Middlesex County schools.

Brian Sicknick, 42, grew up in South River in central Jersey and joined the National Guard in 1997, eventually serving overseas in Saudi Arabia and Kyrgyzstan, NJ.com reported.

Sicknick was honorably discharged in 2003, and began working for the Capitol Hill police force in 2008, most recently in its First Responder Unit, the police department said.

Capitol Hill Police Officer Brian Sicknick

USCP/UPI/Shutterstock

On Wednesday, he was “responding to the riots” as supporters of President Donald Trump rampaged into the Capitol and “was injured while physically engaging with protesters,” the Capitol Police said in a press release Thursday. “He returned to his division office and collapsed. He was taken to a local hospital where he succumbed to his injuries.”

While the Capitol Police did not specify Sicknick’s injuries or cause of death, the New York Times reported that “he was struck with a fire extinguisher, according to two law enforcement officials.”

The Capitol Police did not release details of where Sicknick was in the Capitol when he was attacked, but a New York Post reporter inside the building Wednesday posted video online of the Trump supporters discharging a fire extinguisher outside Senate Chambers.

Sicknick's brother Ken Sicknick said in a statement, "Many details regarding Wednesday's events and the direct causes of Brian's injuries remain unknown and our family asks the public and the press to respect our wishes in not making Brian's passing a political issue," NJ.com reported. "Please honor Brian's life and service and respect our privacy while we move forward in doing the same. Brian is a hero and that is what we would like people to remember. Thank you."

Sicknick was the fifth fatality linked with the violent insurrection by pro-Trump supporters at the Capitol Wednesday. A California woman was fatally shot by law enforcement as she apparently tried to climb through a broken window to gain access to a barricaded hallway next to the House of Representatives chamber where some lawmakers were gathered, the Washington Post reported.

Three other people who attended the protest died of “medical emergencies,” the Metropolitan Police Department announced, though it’s unclear where they were on Capitol grounds at the time of their deaths.

About 50 law enforcement officers suffered injuries as the Trump supporters “swarmed barricades, threw objects, battered doors, smashed windows and overwhelmed some of the officers who tried to resist the advancing crowd,” the New York Times described, and two people were arrested for assaulting an officer.

The US Attorney’s office plans to open a federal murder investigation into Sicknick’s death, CNN reported. The Metropolitan Police Department’s Homicide Branch and the Capitol Police are also investigating.

In a statement Friday, New Jersey Governor Phil Murphy called Sicknick’s death a “needless murder at the hands of a mob bent on overthrowing the Constitution he had dedicated his life to upholding.”

Murphy thanked Sicknick for his service, noting that “he was a Fire Team Member and Leader with the 108th Security Force Squadron, 108th Wing, at Joint Base McGuire-Dix-Lakehurst” during his time with the New Jersey National Guard. “Officer Sicknick gave his life protecting the United States Capitol, and by extension, our very democracy, from violent insurrection,” Murphy said.

Sicknick is the fourth officer killed in the line of duty in the Capitol Police’s two-century-long history.