U.S. Capitol Police Chief Steven Sund is resigning after receiving criticisms on the department's response to rioters who breached the Capitol in protest of President Donald Trump's election loss against President-elect Joe Biden.

Aside from the Capitol police chief's resignation, a police officer died following the riots in the area, according to U.S. Capitol Police in a statement late Thursday night.

The officer was identified as Brian D. Sicknick, a 15-year veteran of the force and 40 years old, WUSA 9 reportedNo information was released on where the officer was stationed around the Capitol on Wednesday as a mob of Trump supporters forced entry into the Capitol. 

Police said Sicknick was injured while physically engaging with protesters, and he collapsed after he returned to his division office and was taken to a hospital. He died on Thursday night.

The news on the officer's condition came minutes after Sund's resignation. With Sicknick's death, at least five people already died in the mayhem in Washington, D.C.

Capitol Police Chief Resignation

According to the police spokeswoman on Thursday, Sund's resignation would take effect on Jan. 16, a few days before President-elect Joe Biden's inauguration.

In a statement, the force's union Chairman Gus Papathanasiou said that the officers are frustrated and demoralized how a lack of leadership undermined the response to the mob.

But the chairman noted that they prioritized lives over the property, leading people to safety. Papathanasiou's said not one member of Congress or their staff was injured, showing that the officers did their jobs, NBC News reported.

Capitol police received a backlash for its inability to keep rioters out of the building. Biden earlier compared how police treated the pro-Trump mob versus how they treat the Black Lives Matter movement's supporters over the summer. Biden described the treatment as double standards.

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House Speaker Nancy Pelosi also called on Sund to resign earlier Thursday, while a bipartisan group asked for an investigation into law enforcement's response to the riots.

According to a Forbes report, the lawmakers' bipartisan group includes Senate Majority Leader Mitch McConnell and Rep. Ilhan Omar.

Capitol Police reportedly turned down extra workforce in the days before the planned demonstration in Washington D.C. The police force also appeared to be unprepared and was overwhelmed by the number of Trump supporters, who breached their way into the Capitol Building. 

Capitol Police's Unpreparedness

A law enforcement official said the Capitol Police seemed to have little resistance and arrested only 14 people, making it more difficult to find and charge other rioters.

The New York Times reported that policing experts also cited the absence of crowd-control gears such as mounted officers, police dogs, or a heavily manned perimeter.

On Thursday, Pentagon authorities said that Capitol Police had turned down an offer for additional National Guard troops before Wednesday's Capitol breach.

Also, two law enforcement officials said they initially snubbed help from the Federal Bureau of Investigation as the mob descended. Charles Ramsey, a former D.C. police chief, said the police seemed to be "not ready for this day." 

"They were overwhelmed; they did not have the resources. You have to be able to protect the Capitol," Ramsey told the New York Times.

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