Capitol Police Chief Steven Sund announced his resignation Thursday, a day after protesters breached the Capitol, overran his officers and prompted condemnations from lawmakers on both sides of the aisle in Washington, including a call for him to step down from House Speaker Nancy Pelosi.

"It has been a pleasure and true honor to serve the United States Capitol Police Board and the Congressional community alongside the women and men of the United States Capitol Police," he wrote.

He said the resignation would take effect Sunday, Jan. 16.

During a news conference about charges against the rioters earlier in the day, Acting U.S. Attorney for the District of Columbia Michael Sherwin had said that the Capitol Police’s handling of the breach "made our job more difficult."

LAWMAKERS, AIDES AND OTHERS SHELTERING INSIDE CAPITOL DESCRIBE CHAOS

"Why they (those who broke in) weren't zip-tied as they left the building, I don’t know," Sherwin said.

UNITED STATES - FEBRUARY 11: Chief Steven A. Sund testifies during the House Appropriations Legislative Branch Subcommittee hearing on the U.S. Capitol Police FY2021 Budget Request, in the Capitol on Tuesday, February 11, 2020. (Photo By Tom Williams/CQ-Roll Call, Inc via Getty Images) (Getty Images)

In a statement, the D.C. Police Union, which represents the city’s Metropolitan Police Department, not its counterparts on Capitol Hill, said its officers responded after Capitol Police called for backup.

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"When we arrived, it was obvious that our fellow officers of the U.S. Capitol Police were trying valiantly to stop the onslaught of rioters," the union said. "While it is unclear at this preliminary stage exactly how the building was breached so quickly, it appears likely that U.S. Capitol Police leadership was ill-prepared for this attack, both in manpower and in resources."

At least four people died, according to authorities.

They were a California woman who was shot by police at a barricaded doorway and three other individuals who succumbed to medical emergencies during the mayhem.

Capitol Police identified Ashli Babbitt as the person shot. She was a 14-year Air Force veteran from San Diego.

Ashli Babbitt has been identified as the woman shot dead inside the U.S. Capitol on Wednesday. (WTTG-TV)

Video shows a woman collapsing in the hallway before a man in a suit and nearby officers rendered aid, but police said she later died in the hospital.

The officer involved in the shooting has been placed on administrative leave and an investigation has begun.