BOSTON — There’s little doubt the Oath Keepers were planning for something on Jan. 6. The question at the heart of the criminal case against its members and associates in the attack on the U.S. Capitol is: What, exactly, did they intend to do?

Authorities suggested for weeks in court hearings and papers that members of the far-right militia group plotted their attack in advance in an effort to block the peaceful transition of power. But prosecutors have since said it is not clear whether the group was targeting the Capitol before Jan. 6.

“The plan was to unlawfully stop the certification of the Electoral College vote … and the plan was to be prepared to use violence if necessary,” Assistant U.S. Attorney Kathryn Rakoczy said during a hearing this month. But the Oath Keepers “did not know precisely the way in which force and violence might be needed to support this plan,” she said.

Authorities are still combing through a sea of evidence in what they say is likely the most complex investigation ever prosecuted by the Justice Department. More than 300 people are facing federal charges and more are expected. The most serious charges have been brought against 10 people described as members and associates of the Oath Keepers and several members of another far-right extremist group, the Proud Boys.

But as the sprawling investigation has unfolded, prosecutors have sometimes struggled to maintain a consistent narrative and had to walk back statements made in court hearings or in papers. It has created an opening for defense attorneys to try to sow doubt in the case.

“The government presented a theory (without evidence) that there was a weeks long plan to invade the Capitol,” an attorney for one of the Oath Keepers, Jessica Watkins, wrote in a recent court filing. “There was no such plan.”

In one case, prosecutors declared in court documents in January there was “strong evidence” the pro-Trump mob aimed to “capture and assassinate elected officials.” The Justice Department quickly clarified it had no such evidence, blaming it on a miscommunication between prosecutors.

After she was pressed by a judge in a recent hearing, Rakoczy conceded authorities “do not have at this point someone explicitly saying, ‘our plan is to force entry into the Capitol in order to stop the certification,’” but cautioned that the investigation is ongoing.

“Part of the reason that there wasn’t necessarily as concrete a plan that one might expect is that they were waiting and watching to see what leadership did,” she said.

Just a month earlier, Rakoczy told the same judge there’s no other way to read the group’s messages about stationing a “quick reaction force” outside the city other than that they needed weapons available “in the event the activities at the Capitol went badly.”

“And those activities at the Capitol were a planned and very well-coordinated attack on the United States Capitol,” she said.

Defense attorneys argue any discussions their clients had before Jan. 6 were in reference to providing security at the rally before the riot or protecting themselves against possible attacks from antifa activists.

The defendants can still be convicted of conspiring to obstruct Congress even if the plan was formulated only moments before they stormed the Capitol, said Jimmy Gurule, a former federal prosecutor who’s now a professor at the University of Notre Dame law school. And prosecutors have some “pretty compelling circumstantial evidence,” he said.

Communications detailed in court documents show the group discussing things like gear and training in the weeks leading up to Jan. 6. One man suggested getting a boat to ferry weapons across the Potomac River into their “waiting arms,” authorities say.

In December, Kelly Meggs, who officials say was the leader of the Oath Keepers’ Florida chapter, wrote in a message that he had “organized an alliance” with the Proud Boys. Days before Jan. 6, Meggs instructed someone to tell their friend “this isn’t a rally,” authorities say.

Many came dressed for battle on Jan. 6 in tactical vests and helmets. The leader of the Oath Keepers, who has not been charged, communicated with some of the defendants over a Signal chat called “DC OP: Jan 6 21,” which prosecutors say shows the group was “activating a plan to use force on Jan. 6.”

Authorities wrote in court papers that the group not only conspired to “forcibly storm the U.S. Capitol on January 6, 2021 — they planned their attack in advance.” The evidence is “irrefutable,” prosecutors wrote in another document, that Watkins “recruited others to join, trained for, planned, and participated in a coordinated effort to, as she put it, ‘forc(e) entry into the Capitol Building.’”

U.S. District Judge Amit Mehta agreed in February to keep Thomas Caldwell, who authorities have portrayed as a leader of the conspiracy, locked up while he awaits trial, saying the evidence showed he “engaged in planning and communications with others … to plan a potential military-like incursion on the Capitol on January the 6th.”

But after Caldwell’s lawyer challenged that assessment, the judge reversed his decision and released Caldwell to home confinement. Mehta said there’s no evidence he entered the Capitol on Jan. 6 or had been plotting to do so.

“Last time we were here 30 days ago, I was convinced that it was a plan to execute an incursion on the Capitol building,” the judge told Caldwell’s attorney. “You’ve raised some evidence that, I think, rebuts that notion.”

The judge has since released other defendants, noting there’s no evidence they assaulted anyone at the Capitol or, in some cases, don’t appear to be as involved in the planning before Jan. 6.

But Mehta on Friday ordered Meggs to remain locked up, calling him a danger to the community. The judge said his communications in the weeks leading up to the attack show he was planning for violence in the streets of Washington even if none specifically mention a plot to storm the Capitol.

Prosecutors have also apparently been unable to get on the same page about what to say to the press.

A judge recently scolded the Justice Department over a “60 Minutes” interview during which the prosecutor who was leading the investigation suggested some of the rioters could face sedition charges. Former acting District of Columbia U.S. Attorney Michael Sherwin’s interview appeared to violate Justice Department rules and Sherwin is now under internal investigation, a prosecutor told the judge.