Former President Donald Trump pleaded not guilty in June to a 37-count indictment related to his handling of classified materials, after prosecutors said he repeatedly refused to return hundreds of documents containing classified information ranging from U.S. nuclear secrets to the nation's defense capabilities, and took steps to thwart the government's efforts to get the documents back.

Efforts to retrieve the documents began in early 2022 when officials with the National Archives said they had retrieved 15 boxes of presidential records that Trump had "improperly" taken to his Mar-a-Lago estate after leaving the White House. Trump was then subpoenaed for the return of additional documents authorities said he still possessed.

In June, federal agents visited Mar-a-Lago to search for additional materials, after which prosecutors said an attorney for Trump signed a statement attesting that all classified documents at Mar-a-Lago had been turned over to federal investigators. Two months later, FBI agents raided the South Florida estate and found more than 100 additional documents with classified markings that had not been turned over.

In November, Attorney General Merrick Garland appointed a special counsel to investigate.

Here's a look at how the probe has progressed.

Nov. 18, 2022

Attorney General Merrick Garland taps Jack Smith as special counsel to oversee the Justice Department's criminal investigation into the unlawful retention of national defense information at Trump's Mar-a-Lago estate as well as the investigation into efforts to overturn the 2020 election. The announcement is triggered when Trump's announcement that he is running for president for a third time creates a potential conflict of interest with the Justice Department.

Smith previously served as the chief prosecutor for the special court in The Hague charged with investigating war crimes in Kosovo.

Dec. 1, 2022

A panel of judges on the 11th U.S. Circuit Court of Appeals overturns the appointment of a special master who had been tasked by U.S. District Judge Aileen Cannon with reviewing thousands of documents seized by the FBI from Mar-a-Lago to identify personal documents and potentially privileged material.

The order effectively eliminates what federal authorities had described as a major obstacle in their ongoing criminal probe.

Dec. 22, 2022

Top Trump attorney Timothy Parlatore appears before the grand jury probing Trump's handling of classified documents to provide information about efforts by Trump's team to locate any classified documents that remained in Trump's possession after the FBI's August raid of Mar-a-Lago, according to what sources later tell ABC News.

Feb. 14, 2023

ABC News reports that investigators have asked a judge to overrule attorney-client privilege and compel Trump attorney Evan Corcoran to appear before the grand jury probing Trump's handling of classified documents, according to sources.

According to a previous DOJ filing, Corcoran was one of the Trump attorneys who certified to investigators in early June that a "diligent search" of Mar-a-Lago turned up just 38 classified documents -- two months before FBI agents raided the premises and found more than 100 additional classified documents.

March 16, 2023

ABC News reports that Smith is pushing to question Corcoran about an alleged phone call he and Trump had as investigators were building evidence about Trump's potential obstruction of the government's efforts to retrieve classified materials, according to sources.

March 17, 2023

Prosecutors in the special counsel's office have presented compelling preliminary evidence that Trump knowingly and deliberately misled his own attorneys about his retention of classified materials after leaving office, a top federal judge writes in a sealed filing, according to sources.

U.S. Judge Beryl Howell writes that prosecutors had made a "prima facie showing that the former president had committed criminal violations," according to the sources, and that attorney-client privileges invoked by two of his lawyers could therefore be pierced. The ruling compels Corcoran to provide additional testimony before a federal grand jury investigating Trump's handling of classified documents, per sources.

March 24, 2023

Corcoran, following Judge Howell's orders, appears before the grand jury probing Trump's handling of classified documents, according to sources.

April 3, 2023

Multiple U.S. Secret Service agents connected to Trump's security detail have been subpoenaed by the special counsel, a source tells ABC News.

May 17, 2023

ABC News reports that top Trump attorney Tim Parlatore, who has played a central role in the investigation into Trump's handling of classified documents, has departed the former president's legal team.

May 23, 2023

Trump's legal team formally requests a meeting with Attorney General Merrick Garland amid concerns from Trump's attorneys that the coming weeks could bring a possible indictment of Trump regarding his handling of classified materials.

May 31, 2023

ABC News reports that federal investigators have in their possession an audio recording of Trump from a July 2021 meeting at his Bedminster, New Jersey, golf club, on which he appears to acknowledge possessing a sensitive military document that he retained after leaving office, according to sources

Trump indicated on the recording that he knew the document in question was secret, the sources said.

June 5, 2023

Lawyers for Trump meet with officials at the Department of Justice, according to sources. Afterward the attorneys decline to answer ABC News' questions about whether they were informed that a charging decision has been made regarding Trump's handling of classified documents.

June 6, 2023

ABC News reports that Trump's last White House chief of staff, Mark Meadows, has testified before the grand jury, according to sources.

June 7, 2023

ABC News reports that Trump recently received a letter from the special counsel office informing him that he is a target in their classified documents probe, according to sources.

Earlier in the day, former Trump aide and MAGA Inc. super PAC founder Taylor Budowich appears before the grand jury, Budowich confirms on Twitter.

June 9, 2023

Trump is hit with a sweeping 37-count indictment from the special counsel's office, alleging that he willfully retained documents containing the nation's most sensitive secrets, including nuclear programs, after he left office, showed some of them on at least two occasions, and then tried to obstruct the investigation into their whereabouts.

The indictment also charges longtime Trump aide Walt Nauta in connection with the handling of government documents.

June 13, 2023

Trump is arraigned in a federal courtroom in Miami on 37 counts: 31 counts of willful retention of national defense information; one count of conspiracy to obstruct justice; one count of withholding a document or record; one count of corruptly concealing a document or record; one count of concealing a document in a federal investigation; one count of scheme to conceal; and one count of false statements and representations.

He enters a not guilty plea through his attorneys and does not speak during the court appearance. Later, speaking at his golf club in Bedminster, New Jersey, Trump calls the charges "the most evil and heinous abuse of power in the history of our country" and says "I had every right to have these documents."

June 15, 2023

ABC News reports that last fall, Trump rejected a proposal from one of his attorneys who was attempting to keep charges off the table in the special counsel documents probe, according to sources.

The attorney, Christopher Kise, wanted to propose a settlement with the Justice Department that would preclude charges, but the idea was quickly shut down by Trump and some members of his team who backed a more adversarial approach to federal investigators, the sources said.

June 19, 2023

In an interview on Fox News, Trump says the material he displayed at a July 2021 meeting at Bedminster was not a classified document as he allegedly appeared to suggest in a recording of the meeting obtained by investigators.

"There was no document," he tells Fox News' Bret Baier. "That was a massive amount of papers and everything else talking about Iran and other things. And it may have been held up or may not, but that was not a document. I didn't have a document per se. There was nothing to declassify. These were newspaper stories, magazine stories and articles."

June 20, 2023

U.S. District Judge Aileen Cannon sets a tentative date of Aug. 14 for the start of Trump's trial on charges of obstruction and mishandling classified documents.

The judge riles the trial will take place at the Fort Pierce, Florida, courthouse -- not in Miami where Trump's initial appearance and arraignment took place.

June 23, 2021

The special counsel asks Judge Cannon to delay the start of the trial until December, citing the need for defense counsels to obtain the necessary security clearances before they can review discovery materials.

June 26, 2023

ABC News obtains the audio recording from the July 2021 meeting at Bedminster in which Trump is heard displaying what appears to be a sensitive military document and acknowledging that he hadn't declassified it.

"It is like, highly confidential. Secret. This is secret information," Trump is hear saying. "Look, look at this. This was done by the military and given to me. As president I could have declassified, but now I can't."

Prosecutors say that Trump's acknowledgement on the recording that he could no longer declassify the document undercuts his contention that he had declassified all the documents in his possession before leaving the White House.

June 28, 2023

ABC News reports that Susie Wiles, one of the top adviser leading Trump's reelection effort, is among the individuals identified but not named by the special counsel in his indictment against the former president, according to sources.

Trump, in the indictment, is alleged to have shown a classified map of an unidentified country to Wiles while discussing a military operation that Trump said "was not going well," while adding that he "should not be showing the map" to her and "not to get too close."

July 6, 2023

Nauta pleads not guilty to all charges at his arraignment in Florida. The longtime Trump aide appears in a Miami federal courthouse after his scheduled arraignment was repeatedly delayed due in part to his inability to obtain local counsel to represent him.

His plea is entered by Trump attorney Stan Woodward, and Nauta is represented by Woodward and local Florida attorney Sasha Dadan.

July 10, 2023

In a court filing, lawyers for Trump ask Judge Canon for a lengthy delay to Trump's trial, suggesting it would not be possible to try the case prior to the 2024 election.

July 14, 2023

ABC News reports that the special counsel recently transmitted a target letter threatening potential charges against a Trump Organization employee who is suspected of lying to investigators, according to sources. Investigators have been scrutinizing the employee's role in the handling of surveillance footage at Trump's Mar-a-Lago estate that was sought by federal prosecutors last summer, sources said.

July 21, 2023

Striking a compromise between the special counsel and Trump's attorneys, Judge Cannon schedules Trump's classified documents trial to start on May 20.

The date is later than prosecutors had sought but sooner than the indefinite delay requested by Trump.

July 27, 2023

A grand jury returns a superseding indictment containing additional documents-related charges against Trump and two others.

Carlos De Oliveira, the head of maintenance at Mar-a-Lago, is added to the obstruction conspiracy charges as prosecutors allege that he, Trump and Nauta conspired to delete footage from Mar-a-Lago's security cameras that allegedly showed employees moving around boxes containing classified materials. The indictment lays out a timeline of events that prosecutors say shows what took place.

It also charges Trump with allegedly possessing the classified document that he was heard discussing on the audio recording of the July 21, 2021, meeting at Bedminster.

July 28, 2023

Trump tells radio host John Fredericks that he'll continue to run for president even if convicted and sentenced on criminal charges brought by the special counsel.

"If going forward, right, you get these indictments, there ends up -- you got a jury in D.C., you get convicted and sentenced -- does that stop your campaign for president if you're sentenced?" Fredericks asks Trump in an interview.

"Not at all," Trump replied. "There's nothing in the Constitution to say that it could, and not at all."

July 31, 2023

De Oliveira makes his initial court appearance in Miami but cannot be arraigned because he does not have local counsel. The Mar-a-Lago property manager is released on a $100,000 personal surety bond.

Aug. 7, 2023

Judge Cannon raises questions about Smith's use of another grand jury to purportedly continue to investigate Trump's alleged mishandling of classified documents after leaving office, even though Trump has already been indicted on charges by a separate grand jury impaneled in Florida.

In a ruling, the judge asks Nauta's attorney, Stanley Woodward, to file a motion stating his concerns about "the legal propriety of using an out-of-district grand jury proceeding."

Aug. 9, 2023

Trump's attorneys ask Judge Cannon to approve a special facility at Mar-a-Lago for him to be able to discuss classified evidence with his legal team "as necessary to prepare an adequate defense," they say in a legal filing.

Trump's team specifically asks that a previous facility Trump used at Mar-a-Lago while serving as president -- where he was previously permitted to discuss and review classified information -- be re-established so he can now discuss classified discovery materials shared by the special counsel.

Aug. 10, 2023

Trump, through his attorney, and Nauta, appearing in person, both plead not guilty in a Florida courtroom to new charges brought by the special counsel in his superseding indictment. De Oliveira still cannot be arraigned because arrangements for local counsel have not yet been finalized.

Aug. 14, 2023

In a court filing responding to Trump's request for a secure facility at Mar-a-Lago to discuss classified discovery evidence with his legal team, the special counsel's office says that such a facility would be an "unnecessary and unjustified accommodation."

Aug. 15, 2023

De Oliveira, appearing in a Fort Pierce, Florida, courtroom with local counsel, pleads not guilty to all charges brought by Smith in the superseding indictment. The four criminal counts include making false statements, conspiring to obstruct justice, and altering, destroying, mutilating or concealing an object from an official proceeding.

Aug. 17, 2023

ABC News reports that special counsel Jack Smith earlier in the year sought extensive data, including direct messages, tied to Trump's account on X, formerly known as Twitter, according to new court filings.

Aug. 20, 2023

ABC News reports that, appearing to contradict Trump's primary public defense in the classified documents case, former Chief of Staff Mark Meadows has told special counsel investigators that he could not recall Trump ever ordering, or even discussing, declassifying broad sets of classified materials before leaving the White House, nor was he aware of any "standing order" from Trump authorizing the automatic declassification of materials taken out of the Oval Office, according to sources.

Aug. 22, 2023

ABC News reports that a Mar-a-Lago Information Technology worker's decision to cooperate with the special counsel and change his previous testimony paved the way for prosecutors to seek new obstruction charges against Trump and two other aides in July's superseding indictment, according to sources.

The IT director, whose identity is confirmed by sources as Yuscil Taveras, is set to be a central witness for Smith in his case against Trump, Nauta and De Oliveira, sources say.

Sept. 6, 2023

ABC News reports that Trump was warned the FBI could raid Mar-a-Lago if he didn't comply with a DOJ subpoena, according to voice memos made last May by Trump attorney Evan Corcoran and reviewed by ABC News.

Sept. 18, 2023

ABC News reports that one of Trump's long-time assistants told federal investigators that Trump repeatedly wrote to-do lists for her on documents from the White House that were marked classified, according to sources.

Sept. 28, 2023

ABC News reports that Trump's legal team has asked the judge in the case for a three-month delay to deal with issues related to their ability to view the classified information at the center of the case.

Special counsel Jack Smith's 's office says in a filing that some documents are so sensitive that they cannot be stored in a secure facility in Florida with the other documents in the case, and therefore must be viewed in a secure facility in Washington, D.C.

Oct. 5, 2023

ABC News reports that months after leaving the White House, Trump allegedly discussed potentially sensitive information about U.S. nuclear submarines with a member of his Mar-a-Lago Club -- an Australian billionaire who then allegedly shared the information with scores of others, including more than a dozen foreign officials and a handful of journalists, according to sources, who say the potential disclosure was reported to Jack Smith's team.

Oct. 6, 2023

Judge Cannon pauses any litigation involving the classified materials at the center of the case as she considers a request from Trump to extend deadlines in the case, according to a court order.

Oct. 12, 2023

The special counsel's team argues at a hearing that attorneys representing Nauta and De Oliveira could have conflicts of interest due to their past and current representations of witnesses who the government may call at trial -- but Judge Cannon chastises prosecutors for making what she calls "last minute" arguments, and dismisses the hearing until a later date.

Oct. 20, 2023

Walt Nauta tells Judge Cannon that he wants his attorney Stanley Woodward to continue to represent him in the case despite any potential conflicts Woodward has with his previous and current representations of witnesses in the case.

Oct. 31, 2023

Trump joins his attorneys in Miami for a visit to a Sensitive Compartmented Information Facility -- or SCIF -- in order to view the classified evidence shared by the special counsel as part of his case against Trump, according to sources.

Nov. 1, 2023

Saying that all the necessary preparations could be hard to do "in a compressed period of time," Judge Cannon says that she'll make "adjustments" to the case's schedule, acknowledging that the trial could collide with the trial date set in Trump's federal election interference case in Washington, D.C.

Nov. 10, 2023

Judge Cannon grants a request from Trump's legal team to push back some pretrial deadlines, but keeps the trial's May start date for the time being.

Nov. 29, 2023

ABC News reports that Trump attorney Jennifer Little told the special counsel's team earlier in the year that, within days of the Justice Department issuing a subpoena for all classified documents at Trump's Mar-a-Lago estate, she "very clearly" warned Trump that if he failed to fully comply -- but then swore he did -- "it's going to be a crime," according to sources familiar with the matter.

Feb 1, 2024

ABC News reports that, according to sources, the special counsel's team questioned several witnesses about a closet and a so-called "hidden room" inside Trump's residence at Mar-a-Lago that the FBI didn't check while searching the estate in August 2022.

Sources said the line of questioning came in several interviews ahead of Trump's June 2023 indictment on classified document charges, suggesting that after the FBI seized more than 100 documents marked classified from Mar-a-Lago, the special counsel was trying to determine if there might still be more classified documents there.

Feb 8, 2024

The special counsel's team says it is investigating a series of threats made online to a potential witness related to the classified documents case, according to a court filing. The special counsel asks Judge Cannon to let them file an exhibit under seal because, they say, "Disclosure of the details and circumstances of the threats risks disrupting the investigation."

Feb 9, 2024

The special counsel, in a court filing, accuses Trump of a "relentless and misleading" ploy to delay his trial from the scheduled May 20 start date.

Feb 12, 2024

Trump spends about four hours at a hearing in the case held in a special secure facility due to the sensitive nature of the classified materials at issue.

Feb 22, 2024

Trump's legal team files a series of motions to dismiss the case, arguing that it should be dismissed on the grounds of presidential immunity; that Jack Smith's appointment as special counsel was unlawful; that Smith charged Trump with statutes that shouldn't apply to the former president's behavior based on an unclear precedent in the Constitution; and that Trump should have been able to have custody of the documents in question, even after he was president, because of the Presidential Records Act.

March 1, 2024

During a hearing attended by both Donald Trump and Jack Smith, Judge Aileen Cannon hears arguments over moving the case's May 20 trial date.

March 7, 2024

Special counsel Jack Smith issues a wave of responses to what he calls "frivolous" and "outlandish" efforts by Trump to have his classified documents case dismissed before trial.

March 14, 2024

Judge Cannon denies Trump's motion to dismiss the case based on unconstitutional vagueness, one of the two motions -- the other being his protection under the Presidential Records Act -- that his lawyers are using to argue for dismissal.

March 18, 2024

Judge Cannon asks attorneys for both Trump and the special counsel to submit proposed jury instructions on topics relating to Trump's motions to dismiss the case, specifically involving the Presidential Records Act.