April 22 (Reuters) - The U.S. Justice Department expects to charge at least 100 more people for taking part in the deadly attack on the U.S. Capitol, signaling prosecutors are far from finished investigating an attack that a judge on Thursday called an act of terrorism.
"Over 400 individuals have been charged in connection with the Capitol attack," federal prosecutors said in a court filing on Thursday. "The investigation continues and the government expects that at least one hundred additional individuals will be charged."
The Justice Department made the disclosure in a set of similar court filings asking judges to postpone deadlines in pending prosecutions.
"The investigation and prosecution of the Capitol attack will likely be one of the largest in American history, both in terms of the number of defendants prosecuted and the nature and volume of the evidence," the court filings stated.
Supporters of former President Donald Trump on Jan. 6 stormed the Capitol in an attempt to stop Congress from formally certifying President Joe Biden's election victory.
The violence started shortly after Trump rallied his supporters and urged them to fight to stop the certification of Biden's win.
The siege left five people dead and more than 130 police officers injured.
A magistrate judge in U.S. District Court for the District of Columbia described the attack as an act of terrorism during a court hearing for Charles Donohue, a leader of the Proud Boys extremist right-wing group.
"The acts alleged in the indictment would meet, in my view, the statutory definition of a federal crime of terrorism," U.S. Magistrate Judge G. Michael Harvey said, adding that the attack "struck at the very heart of our democracy."
The FBI has been increasingly focused on suspects with ties to right-wing extremist groups including the Oath Keepers and the Proud Boys.
More than 40 members or associates of the two groups have been arrested and charged so far.
A founding member of the Oath Keepers last week became the first person to plead guilty to taking part in the riot, and prosecutors have said other defendants are in plea discussions.
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