In the nearly nine months since Jan. 6, federal agents have tracked down and arrested more than 600 people across the United States believed to have joined in the riot at the U.S. Capitol.

Getting those cases swiftly to trial is turning out to be an even more difficult task.

Investigators have collected a mountain of evidence in the attack and are working to organize it and share it with defense attorneys. And that mountain keeps growing with new arrests still happening practically every week.

Washington's federal court, meanwhile, is clogged with Jan. 6 cases, which more than double the total number of new criminal cases filed there all of last year. Further complicating things are limitations the court has put on trials because of the coronavirus pandemic.

The court delays are dragging out a process already called into question by some right-wing lawmakers, who argue it's a waste of time and money to prosecute people accused of low-level crimes. As the court cases continue to stall, so do answers to what happened that day and the possibility for consequences from the most violent assault at the Capitol in a generation. Meanwhile, Democrats in the House are subpoenaing former President Donald Trump's aides and have requested a trove of documents as a select committee also probes the insurrection.

While it's not unusual for federal cases to take a year or more to work through the system, some defense lawyers and judges are raising concerns that defendants with a right to a speedy trial may end up waiting a long time before getting their day in court.

"The reason for the delay has not changed or become even remotely concrete. It remains as amorphous today as it was months ago," an attorney wrote in court documents opposing prosecutors' request to cancel the scheduled November trial for Timothy Hale-Cusanelli, an ex-Army reservist described by co-workers as a known Nazi sympathizer.

So far, only about 80 cases have been resolved by guilty pleas — largely by those who were charged only with misdemeanor offenses. Scores of others face serious felony charges including conspiracy, assaulting officers and obstructing of an official proceeding that call for lengthy sentences behind bars.

The Justice Department has called it the largest investigation in American history, with probes open in 55 out of 56 FBI field offices. Evidence collected in the attack includes thousands of hours of video footage, hundreds of thousands of tips from the public and more than 1 million Parler posts, replies and data. The Justice Department is building massive databases to share all evidence stemming from the attack with defense attorneys.

In the most high-profile case brought so far, involving more than a dozen members and associates of the far-right extremist group the Oath Keepers, prosecutors recently told a judge that a January trial date for the first set of defendants is looking increasingly unrealistic given how much evidence they still need to get into defense attorneys' hands.

U.S. District Judge Amit Mehta said if they have to wait until prosecutors turn over "every single scrap of evidence" they've collected in the Jan. 6 investigation — rather than just that which relates to a specific defendant — there won't be trials in any of these cases before 2023. And three of the Oath Keepers defendants, accused of conspiring to block the certification of Joe Biden's presidential election victory over Trump, are behind bars.

"I have to keep their interests in a speedy trial in mind here," Mehta said. "I am concerned about a lengthy pretrial detention period," he added. He didn't immediately rule but signaled that the first Oath Keepers trial would likely be pushed to April, with the second scheduled for July.

At least one of those roughly 70 defendants who are locked up pretrial has already pointed to the delays in an effort to get out of jail. Kelly Meggs, described by authorities as the leader of the Florida chapter of the Oath Keepers, said in an unsuccessful motion for release that with a January trial looking unlikely, he's effectively being held in "indefinite pre-trial detention which, under the circumstances, is tantamount to a human rights violation."

Prosecutors say they are working as quickly as possible under unprecedented challenges to share all evidence that could potentially help the defense and keep the cases moving forward. But new evidence is still being unearthed with each new arrest or as analysis is completed on the thousands of hours of video taken during that chaotic day.

In the case of Robert Reeder, armchair detectives who call themselves Sedition Hunters unearthed new evidence just before he was supposed to be sentenced last month with a recommendation of probation. The video appears to shows Reeder scuffling with a police officer, running counter to his assertion that he had not been part of any violence that day. Reeder's attorney called the clip problematic. A new sentencing is set for Oct. 8.

The coronavirus is only making matters worse.

Cases were already backed up because of the pandemic, and the court has said no more than three trials can be held at once at least until the end of October to allow for social distancing. A judge in one case recently warned attorneys there's no guarantee they will be going to trial as planned in February if COVID-19 numbers tick up.

The pandemic has also made it harder for defendants held behind bars to safely work with their lawyers — a problem that's plagued the entire criminal justice system.

"The defense attorneys just aren't really able to consistently meet with their clients, aren't able to consistently share data or prepare defense with them in an engaged, consistent way," said Jon Lewis, a research fellow who's been following the Jan. 6 cases for the Program on Extremism at George Washington University. "It's a very real issue."

Some defendants, like Hale-Cusanelli, say they don't want to wait any longer for their chance to defend themselves in court. Hale-Cusanelli is scheduled for trial on Nov. 9, but prosecutors say there's no way that's possible. A judge has set a hearing for next week to decide whether to keep that date in place.

A lawyer for the former Army reservist accused prosecutors of seeking more time only to "further cement their case" against his client, "despite having allegedly sufficient evidence to indict" him. Prosecutors called that assertion "wholly without foundation."

"The government has presented eminently reasonable explanations for the delay: its strenuous efforts to meet the challenges imposed by the enormous amount of relevant evidence that it must review, process, categorize, and organize into a format that will make it accessible and useful to the defense," they wrote in court documents.

Prosecutors say Hale-Cusanelli, who worked as a security contractor at a Navy base, used his military training to avoid the effects of pepper spray and tactical hand signals to urge fellow rioters forward on Jan. 6. He later described the day as exhilarating to a tipster, praising the "the adrenaline, the rush, the purpose" he felt, according to court documents.

Hale-Cusanelli's attorney has noted that he is not accused of hurting anyone that day. The defense has called him an "opinionated individual" who "fully exercised his right to speak freely before being imprisoned."

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Richer reported from Boston, and Whitehurst reported from Salt Lake City.