Eighteen months since a pro-Trump mob ransacked the Capitol and disrupted the peaceful transition of presidential power, prosecutors are closing in on another milestone: 900 arrests.

According to the latest Justice Department figures, more than 855 members of that crowd are facing charges that range from trespassing on restricted grounds to seditious conspiracy. Prosecutors estimate that more than 2,000 people actually entered the Capitol unlawfully that day, which means hundreds more arrests are likely in the months to come.

For a year and a half, the justice system has been slowly grinding through those cases, which have taken on increasing complexity as the House Jan. 6 select committee reveals new details about then-President Donald Trump's own role in fomenting the events of that day.

So far, 325 defendants have pleaded guilty to crimes stemming from the breach of the Capitol, the vast majority to misdemeanor crimes. But the most crucial tests of the Justice Department's work are still to come. The ongoing hearings of the Jan. 6 panel have produced compelling testimony that points toward Trump's knowledge of the potential for violence, and the trials of the Oath Keepers and Proud Boys -- groups accused of conspiring to violently prevent the transfer of power -- are still months away.