Mourning has begun in Congress for Capitol Police Officer Brian D. Sicknick, who died Thursday from injuries sustained while defending the Capitol from a violent mob.

Speaker Nancy Pelosi ordered the flags at the Capitol lowered to half-staff, and dozens of lawmakers released statements condemning violence and thanking officers for their service. Late Thursday night, many law enforcement officers were seen parking vehicles in a line to hold a moment of silence — the blue and red lights silently flashed in front of the golden glow of the illuminated Capitol Dome.

Sicknick, 42, was on duty Wednesday when pro-Trump rioters entered the building, vandalizing property and leaving lawmakers terrified. He was injured while “physically engaging with protesters,” a Capitol Police statement said. The military veteran returned to his division office and collapsed. He was taken to a local hospital, where he later died.

“The entire USCP Department expresses its deepest sympathies to Officer Sicknick’s family and friends on their loss, and mourns the loss of a friend and colleague,” the statement said.  

The FBI and Metropolitan Police Department are jointly investigating the case, “and the Department of Justice will spare no resources in investigating and holding accountable those responsible,” a Friday statement from Acting Attorney General Jeffrey A. Rosen said.

The New Jersey native, who lived in Springfield, Virginia, had most recently served as a member of the Capitol Police’s First Responders Unit.

“My brother Brian was the youngest of three sons” and always wanted to be a police officer, his sibling Ken 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,” he wrote. “Brian is a hero and that is what we would like people to remember.”

Born in South River, New Jersey, Sicknick joined the Air National Guard in the late 1990s and was deployed to Saudi Arabia. 

Later, he became a special police officer at Andrews Air Force Base in Maryland. After the 9/11 attacks, he was deployed to Kurdistan as part of Operation Enduring Freedom. He joined the Capitol Police in 2008.

He was a private person, according to a statement released by his family, but had a softer side and was committed to rescuing Dachshunds in his spare time. A hockey fan, he enjoyed watching the New Jersey Devils or movies at home with his girlfriend of 11 years, Sandra Garza.

Sicknick also leaves behind his parents, Charles and Gladys, and his brothers Ken and Greg.

The death ends a turbulent week for the Capitol Police in which rank-and-file officers faced off with rioters in the historic building, while leaders of the force drew stinging criticism for failing to prevent the attack. Lawmakers from both parties simultaneously praised the bravery of those tasked with protecting the congressional campus and fumed that higher-ups should have been better prepared. Five people have died, including a woman shot by Capitol Police and others from medical emergencies.

Taking his cue from Pelosi, who called on him to resign, Capitol Police Chief Steven A. Sund announced he would step down effective Jan. 16.

Majority Leader Mitch McConnell released a statement Thursday applauding the front-line law enforcement officers who came to the aid of Capitol Police officers to help “subdue the criminals and retake the Capitol.”

The Kentucky Republican said investigations were coming to understand, address and fix the “shocking failures in the Capitol’s security posture and protocols.”

Virginia Democratic Rep. Don Beyer, whose office released a statement calling Sicknick his constituent, mourned his death and sent condolences to his family.

“His murder multiplies the pain of this dark moment for our nation, and those who brought about this awful crime must be prosecuted and brought to justice,” Beyer said.

The last time a member of the force was killed defending the Capitol was in 1998, when Officer Jacob J. Chestnut and Detective John M. Gibson were murdered by a gunman attempting to force his way into the building.

Sergeants Christopher S. Eney and Clinton J. Holtz are other officers who have died while serving the force. Eney was accidentally shot during a training exercise in 1984, and Holtz died after a cardiac event in 2014.

Both Gibson and Chestnut lay in honor in the Capitol Rotunda before they were buried in Arlington National Cemetery.

Beyer encouraged leaders to bestow similar honors on Sicknick, though no announcement has yet been made.

“Like others before him who died in defense of the people’s representatives,” Beyer said, “he deserves to lie in state.”