(Reuters) — The U.S. Justice Department on Friday said it expects to file criminal charges against more than 100 additional people who allegedly participated in the Jan. 6 attack on the U.S. Capitol, in what it described as probably the most complex investigation it has ever handled.

More than 300 people already face charges stemming from the siege, which left five people dead and more than 130 police officers injured as thousands of supporters of former President Donald Trump tried to prevent Congress from certifying his election defeat.

The Justice Department made the disclosure in court filings seeking 60-day extensions in some cases so that investigators can adequately pull together evidence.

“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,” prosecutors said in court filings.

More than 900 search warrants have been executed in almost all 50 states and the District of Columbia, prosecutors said. Investigators have accumulated more than 15,000 hours of video from surveillance and body-worn cameras.

The FBI has been increasingly focused on suspects with ties to right-wing extremist groups like the Oath Keepers and the Proud Boys. Prosecutors have charged nine alleged Oath Keepers with planning the attack as far back as November.

Investigators are also examining the role of pro-Trump speakers and protest organizers, including former Trump adviser Roger Stone and Internet conspiracy theorist Alex Jones, according to a senior law enforcement source.

However, criminal charges are unlikely at this point, the source said.

Stone has acknowledged that Oath Keepers had served as security guards at a rally the day before the attack, but has denied any involvement in the riot.

Jones did not respond to a request for comment.