The special investigation into Russian involvement in the 2016 election has yielded its first charges, according to CNN, and the unnamed defendant or defendants will reportedly be taken into custody Monday.

Aside from the skeletal report, not much is known about the impending arrests, but there are a few clues.

It’s still unconfirmed who’s getting charged or how many people will be involved, but two high profile names have frequently surrounded the investigation: Former Trump campaign manager Paul Manafort and national security adviser Michael Flynn. The FBI raided Manafort’s home in Virginia over the summer, indicating they convinced a judge there was probable cause to believe he possessed evidence about a crime.

Last week, Wayne Holland, a realtor who once represented Manafort, testified before the grand jury about a deal they had done in Virginia, Politico reports. And Manafort’s assistant also testified in September.

Flynn’s name has also appeared regularly throughout Mueller’s investigation. He reportedly offered to testify in exchange for immunity in the spring — an offer Mueller declined at the time.

Both men retroactively registered as foreign agents after the investigation began.

Fresh calls for Mueller to resign made the rounds on conservative outlets this week, with Trump allies Sean Hannity and Chris Christie both suggesting Friday the former FBI head should consider resigning. Calls for Mueller to step down intensified after the publication of unsubstantiated allegations claiming he’d overseen a bribery investigation into a Russian firm that eventually won a bid to manage two U.S.-based uranium mines.

Earlier in the day, White House press secretary Sarah Huckabee Sanders told reporters “the real collusion” was between the Clinton campaign and Russia, a reference to recent reports that Clinton’s campaign funded research that led to the controversial Trump-Russia dossier. She also said the president was “confident” the investigation would soon be over, a conclusion she said was “based on fact” and not from speaking to anyone in the Justice Department.

Trump also tweeted this:

As CNN points out, rules governing special prosecutions required Mueller to inform Deputy Attorney General Rod Rosenstein before obtaining the indictments.

And on Friday, a few hours before the charges dropped, U.S. Attorney Dana Boente (who Trump tapped as acting Attorney General before awarding the position to Jeff Sessions) abruptly resigned. He says he plans to stay on, however, until a replacement has been found.