D.C. police sent about 850 officers, nearly one-quarter of its force, to help rescue the U.S. Capitol from the mob that broke in Jan. 6, and the department estimates it cost the District $8.8 million to secure the downtown during the week the insurrection occurred.

Acting police chief Robert J. Contee III, in his opening statement Tuesday before a closed session of the House Appropriations Committee, also said for the first time that a D.C. police officer who had been at the riot committed suicide in the days that followed.

Contee identified the officer as Jeffery Smith. A department spokesman said Smith was a 12-year veteran assigned to patrol in the 2nd District, which includes the neighborhoods of Chevy Chase, Cleveland Park and Georgetown. The Post could not locate Smith’s family Tuesday evening.

Capitol Police were unable to stop a breach of the Capitol. Washington Post reporter Carol Leonnig and a former Senate Sergeant at Arms describe the events. (The Washington Post)

Smith, who died Jan. 15, was the second officer who had been at the Capitol on Jan. 6 to take his life. Capitol Police Officer Howard Liebengood died Jan. 9. Five other people died in the assault, including Capitol Police Officer Brian D. Sicknick, who authorities said was injured during the riot, and a woman fatally shot by a Capitol Police officer inside the building.

“The costs for this insurrection — both human and monetary — will be steep,” Contee said in his remarks, a copy of which was provided by the D.C. police department.

Contee — who described Jan. 6 as a “dark day for our country” — was one of several witnesses at Tuesday's briefing, the start of what is expected to be a long line of congressional inquiries into the failure to prevent breaches by hundreds of supporters of President Donald Trump trying to overturn an election he had lost.

The acting chief of the Capitol Police apologized to lawmakers during Tuesday’s briefing for “failings” that allowed rioters to enter the Capitol, saying the department should have been better prepared for the attack.

Contee sent D.C. officers to help overwhelmed Capitol officers retake control of the building. It took up to eight hours to clear the building and grounds, and by then Contee said 850 D.C. officers had been deployed to the Capitol and an additional 250 to the area around the federal complex.

The chief cautioned that the $8.8 million cost is an estimate that is sure to change, and he said a more detailed financial accounting is forthcoming. He said police and prosecutors will be “engaged for years” investigating and trying insurgents.

Contee said many aspects of local policing will have to be revisited to confront new threats of domestic terrorism, including training that at present “neither anticipates nor prepares” officers for “hours of hand-to-hand combat.”

The chief also said the D.C. police force’s relationship with the myriad federal agencies in the District might be reexamined. “This assault on the Capitol has exposed weaknesses in the security of the most secure city in the country,” Contee told lawmakers.

He said federal and local agencies will now have to consider domestic terrorism as a serious threat, and “harden targets in the federal enclave.” That, Contee said, could make other buildings in the District “more likely targets.”

Karoun Demirjian, Aaron C. Davis, Alice Crites and Julie Tate contributed to this report.