The Jan. 6 investigation is the biggest in U.S. history. It’s only half done.

The city’s federal court system is bracing for many years more of trials stemming from the Jan. 6, 2021, riot at the U.S. Capitol, with new charges possible against as many as 1,000 more people.

In recent months, law enforcement and judicial authorities have engaged in discussions to manage the huge volume of Jan. 6 cases without overwhelming the courthouse where pleas and trials are held, people familiar with the matter said, speaking on the condition of anonymity to discuss internal operations.

“It’s an enormous, enormous case and, by almost any measure, the largest case the Justice Department has ever had,” said Randall Eliason, a former federal prosecutor who now teaches law at George Washington University. “Big criminal investigations that are far less complicated than this often take several years.”

Eliason said that while the riot cases may be about halfway over, there are indications some of the other branches of the investigation — like the false electors scheme or efforts to use Justice Department officials to undo the election results — appear to be further along, because the witnesses now being subpoenaed include some of the most thorny legal matters and the people closest to former president Donald Trump. Those are generally indicators that an investigation is nearing the end of the fact-gathering phase, he said.

“There are a lot of court fights over privilege, and those take time, and you can’t just plow past them and not try to get critical evidence,” Eliason said.

Prosecutors are hopeful many will be incentivized to plead to help manage the crush of cases, which already have strained the court in the nation’s capital. A Washington Post analysis of the cases so far shows defendants who seek a trial rather than plead guilty end up getting about a year of prison time added to their sentences.

To date, roughly 1,000 people have been arrested for their alleged roles in the events of that day. In late October, when the Justice Department had already charged nearly 900 individuals for alleged crimes surrounding Jan. 6, the U.S. Attorney for the District, Matthew Graves, wrote to court officials alerting them that an additional 700 to 1,200 people may be charged.

That means prosecutors expect that the total number of people charged with crimes related to Jan. 6 may be somewhere between 1,600 and 2,100 people, according to people familiar with the letter. The letter was first reported by Bloomberg News.

That calculation does not include what, if any, charges result from the federal special counsel investigation into activities surrounding Trump allies’ efforts to use fake electors or other subterfuge to undo Joe Biden’s 2020 presidential victory.

As of Wednesday, judges had sentenced 408 Jan. 6 defendants, but only 88 of those were for felonies, mostly for one of two charges: obstruction of an official proceeding or assault on law enforcement.

Defendants who pleaded guilty to assaulting the police have received an average sentence about 13 months lower than those convicted at trial, in part because their sentences were reduced when they received credit for accepting responsibility for their actions.

It is common in the federal court system for defendants who take their cases to trial to end up, if convicted, with significantly longer prison sentences as a result — a dynamic often referred to by lawyers as the “trial penalty.” Typically, federal prosecutors offer to recommend a lower prison sentence if defendants agree to plead guilty and save the court system the time and expense of a trial.

The five Jan. 6 defendants who have been convicted at trial of assaulting police have received an average sentence of more than four and a half years in prison.

Defendants convicted at trial of obstructing an official proceeding have earned an average sentence nearly 19 months higher than those who pleaded guilty to the same charge. This has occurred even as the judges in federal district court in D.C. have gone below the sentencing guidelines in 14 of the 17 trial convictions, and below the government’s recommended sentence in all 17 cases. The dozen defendants who have been convicted at trials of obstructing an official proceeding have been sentenced to an average of almost four years in prison.

What’s still unclear is how many of the additional suspects will face misdemeanor versus felony cases, though prosecutors have warned judges that it is likely the percentage of newly charged cases that will be felonies is likely to increase as investigators pursue more serious accusations. So far, about half of the cases have involved at least one felony, and half have charged only misdemeanors.

In follow-up discussions after Graves sent the letter, prosecutors said they would not ramp up the pace of arrests in a way that would swamp the already strained federal courthouse where the cases are being heard, according to people familiar with the matter.

Prosecutors in the letter also said they would update estimated numbers if resources and circumstances changed.

FBI officials have previously notified Congress that “approximately 2,000 individuals are believed to have been involved with the siege” of the U.S. Capitol, though it was unclear at the time from that statement whether that number of people would face criminal charges.

The prospect of another 1,000 cases has been a topic of discussion at the court for months, since the Justice Department received funding in October to hire scores of short-term prosecutors. The concern has been whether the court could process the number of trials likely to result from so many cases.

Officials have already brought in more court reporters to handle the demands for courthouse transcripts, but some officials still worry about the workload in the coming years.

Jay Town, a former U.S. attorney for northern Alabama, said it is hard on all parties to staff up for a “ton of cases.” But many of the Jan. 6 cases are not complex, he said, and prosecutors and judges by now are deeply familiar with the law and evidence, and that practice could speed prosecutions going forward.

If anything, he said, it is harder for new defense attorneys to “start from scratch” and review the mountains of evidence from that day. “There was nothing patriotic about January 6, and so to think you’re continuing your patriotism by being willing to endure a longer sentence, that’s not patriotic either,” he said.

Another factor that has led to possible court delays is a judge’s ruling in March 2022 that a felony charge used in many Jan. 6 cases — obstructing an official proceeding — could not be applied to defendants unless they tampered with official documents or records.

While that ruling is an outlier so far at the courthouse, an appeal of the issue is still pending, and roughly 160 of the people originally charged with that crime are waiting to see how the higher court rules before pleading guilty or resolving their cases. Whenever the appeals court rules, the issue could still wind up before the Supreme Court, which could mean more delays.

Generally, more than 90 percent of federal criminal cases end in guilty pleas without a trial, past studies have shown. To date, all of the Jan. 6 defendants who have chosen to go to trial have been convicted of something.

Some defendants have argued they did nothing wrong, and some of the Jan. 6 perpetrators have argued after pleading guilty that their conduct was justified. Former president Donald Trump has suggested that, if reelected to the White House, he may pardon the Jan. 6 defendants.

“If you think the key charge might not stick, unlike 90 percent of defendants who plead guilty in all other cases, you might choose to keep delaying, delaying, delaying and hoping for the best or that Trump might pardon you,” one court veteran said.

Meghan Hoyer contributed to this report.