Special Counsel Mueller, appointed by Deputy Attorney General Rod Rosenstein to investigate whether and how Russia meddled in the 2016 presidential election, has indicted 33 people and three companies since his work began. He’s secured several convictions and guilty pleas, and some parties have already been sentenced or have completed their sentences. President Donald Trump consistently downplays the investigation, labeling it a “witch hunt,” and denying any “collusion” occurred between his campaign and Russian representatives.

Mueller’s indictments, accepted pleas, and convictions include:

• Michael Flynn, a campaign adviser and briefly Trump’s national security adviser, pleaded guilty to making false statements to the FBI. Flynn’s sentencing slated for late 2018 was delayed after a contentious hearing in which a judge castigated Flynn for appearing to try to walk back his guilty plea in public, although Mueller said he’d provided “substantial assistance.”
• George Papadopoulos, a campaign foreign policy advisor, who admitted he had negotiated with Russians on setting up a meeting between Putin and Trump that never took place. Papadopoulos pleaded guilty. He spent two weeks in jail in late 2018.
• Rick Gates, an assistant campaign manager to and long-time business partner of Paul Manafort, pleaded guilty to limited charges of conspiracy and lying in exchange for an agreement to cooperate in pursing Manafort. Gates has not yet been sentenced because Mueller said he is still helping investigators.
• Manafort was indicted in two jurisdictions on an array of financial, campaign finance, and other charges. A jury convicted him on eight of 18 charges in a first trial, and he pleaded guilty to two others to avoid a second trial. His ultimate sentence remains in flux because Mueller told a court Manafort continued to lie and commit crimes after he pleaded guilty.
• Michael Cohen, Trump’s long-time lawyer and all-purpose fixer, pleaded guilty to tax fraud, bank fraud, campaign-finance violations, and lying to Congress. He was sentenced in December to three years in prison.
• Alex van der Zwaan lied to the FBI about his contacts with Gates, and pleaded guilty. He served 30 days in jail and was then deported to the Netherlands, his home country.

Although other indictments have also been issued, it’s unclear how much work remains for the grand jury to sift through. But the judge’s action indicates that it’s not yet finished.

The special assistant to Chief Judge Beryl Howell confirmed to several media outlets, including The Hill, that a grand-jury extension past the original 18-month period had been granted, but denied a CNN report that the period was six months. Six months is the longest the judge can extend the special counsel’s grand jury.

A prosecutor presents evidence and examines witnesses before a grand jury, the deliberations of which must be kept secret by the participants, though those testifying may reveal their participation. The members of the grand jury can then vote whether an indictment should be issued. A prosecutor can bring charges even if the grand jury doesn’t agree, or can choose not to pursue an indictment a grand jury agrees on.