The Democratic-led U.S. House of Representatives select committee investigating the Jan. 6, 2021, attack on the Capitol has been working for nearly a year, interviewing witnesses and gathering documents in preparation for public hearings, which are set to begin on Thursday.

The following are some facts about the investigation.

Thousands of Trump supporters stormed the Capitol, the home of Congress, in an attempt to prevent formal certification of the Republican then-2020 president’s election loss to Democrat Joe Biden by US lawmakers, causing millions of dollars in damage. Four people were killed on the day of the attack, and one Capitol Police officer who fought the rioters was killed the following day. Four officers have since committed suicide, and 140 others have been injured.

The committee, chaired by Democratic House Speaker Nancy Pelosi, was formed on July 1, 2021, after Republicans blocked the formation of a bicameral commission.

Representative Bennie Thompson, the panel’s chairperson, is one of seven Democrats on the panel, along with Representatives Zoe Lofgren, Elaine Luria, Adam Schiff, Pete Aguilar, Stephanie Murphy, and Jamie Raskin.

The Republican National Committee censured the panel’s two Republicans, Representatives Liz Cheney (vice chairperson) and Adam Kinzinger, for their participation. The RNC had never previously censured a sitting Republican member of Congress.

More than 1,000 depositions and interviews have been taken by the committee and its dozens of investigators. The majority of those interviewed have not been identified, but those who have been identified include Trump’s daughter and close adviser Ivanka Trump, her husband, Jared Kushner, and attorney Rudy Giuliani.

The committee has announced that it has issued 99 subpoenas to compel testimony and obtain documents, and it is known to have issued more that have not been made public.

Subpoenas have been issued to Mark Meadows, a former congressman who served as Trump’s chief of staff; Steve Bannon, a former Trump adviser; Roger Stone, a long-time Republican operative; Trump’s son Eric; major social media firms; and leaders of the far-right Proud Boys and Oath Keepers groups that have backed Trump.

The committee has collected over 140,000 documents and followed up on 472 tips from its tip line.

The House voted overwhelmingly along party lines to recommend contempt of Congress charges against four Trump associates for their refusal to cooperate. Former aides have been urged by Trump to ignore committee subpoenas.

The House recommendation referred the four cases – Bannon, Meadows, and former top Trump administration aides Peter Navarro and Daniel Scavino – to the Justice Department for a decision on whether to file criminal charges, which carry a maximum sentence of a year in prison and a fine of up to $100,000.

The Justice Department has pursued charges against Bannon and Navarro in a case set to go to trial in July. It has not charged Meadows or Scavino.

A fifth person, Jeffrey Clark, a senior Justice Department official during the Trump administration, was also charged by the committee. After Clark agreed to a deposition, the full House never voted on the charges.

Nearly 850 people have been arrested for crimes related to the Capitol attack, with over 250 of them charged with assaulting or impeding law enforcement. Approximately 90 of those have been charged with using a lethal or dangerous weapon or causing serious bodily harm to an officer.

More than 300 people have pleaded guilty to various federal charges, including 59 felonies. Sixteen people who were members of or affiliated with the right-wing Proud Boys and Oath Keepers have been charged with seditious conspiracy, which carries a prison sentence of up to 20 years.

Six individuals have been found guilty at trials.