Donald Trump at his Mar-a-Lago Club in Palm Beach, Fla., in 2016. Jabin Botsford/The Washington Post

Justice Department and FBI investigators have amassed fresh evidence pointing to possible obstruction by former president Donald Trump in the investigation into top-secret documents found at his Mar-a-Lago home, according to people familiar with the matter.

The additional evidence comes as investigators have used emails and text messages from a former Trump aide to help understand key moments last year, said the people, who like others interviewed for this article spoke on the condition of anonymity to discuss an ongoing criminal investigation.

The new details highlight the degree to which special counsel Jack Smith’s investigation into the potential mishandling of hundreds of classified national security papers at Trump’s Florida home and private club has come to focus on the obstruction elements of the case – whether the former president took or directed actions to impede government efforts to collect all the sensitive records.

The emphasis on obstruction marks a key distinction so far between the Mar-a-Lago investigation and a separate Justice Department probe into how a much smaller number of classified documents ended up in an insecure office of President Biden’s, as well as his Delaware home. The Trump investigation is much further along than the Biden probe, which began in November and is being overseen by a different special counsel, Robert K. Hur. Biden’s lawyers say they have quickly handed over all classified documents found in Biden’s possession.

The Trump investigation team has spent much of its time focusing on events that happened after Trump’s advisers received a subpoena in May demanding the return of all documents with classified markings, the people familiar with the matter said. Smith is trying to determine if Trump or others mishandled national security documents, and if there is enough evidence to ask a grand jury to charge him with obstructing the investigation.

The Mar-a-Lago investigation is one of four separate criminal probes involving Trump, who is campaigning for another term in the White House. Trump has been indicted by a New York grand jury that heard evidence about money paid to adult-film actress Stormy Daniels during his 2016 presidential campaign. He is set to make his first court appearance in that case Tuesday. He is also being investigated by the Justice Department and a state prosecutor in Georgia over efforts to block Joe Biden’s victory in the 2020 election.

An FBI spokesman referred questions to a spokesman for the special counsel, who declined to comment.

Trump spokesman Steven Cheung said in a written statement: “The witch-hunts against President Trump have no basis in facts or law. The deranged special counsel and the DoJ have now resorted to prosecutorial misconduct by illegally leaking information to corrupt the legal process and weaponize the justice system in order to manipulate public opinion and conduct election interference, because they are clearly losing all across the board.”

The statement went on to point to the Biden classified documents probe, as well as the investigation of Hillary Clinton’s use of a private email server when she was secretary of state, suggesting that conduct there was worse than anything that happened at Mar-a-Lago. “President Trump is the only leader fighting for the Constitution and to protect the American people from being abused by those who want to destroy our system of government,” Cheung said.

In the classified documents case, federal investigators have gathered new and significant evidence that after the subpoena was delivered, Trump looked through the contents of some of the boxes of documents in his home, apparently out of a desire to keep certain things in his possession, the people familiar with the investigation said.

Investigators now suspect, based on witness statements, security camera footage, and other documentary evidence, that boxes including classified material were moved from a Mar-a-Lago storage area after the subpoena was served, and that Trump personally examined at least some of those boxes, these people said. While Trump’s team returned some documents with classified markings in response to the subpoena, a later FBI search found more than 100 additional classified items that had not been turned over.

Court papers filed seeking judicial authorization for the FBI to conduct the search of Trump’s home show agents believed that “evidence of obstruction will be found at the premises.”

The application for court approval for that search said agents were pursuing evidence of violations of statutes including 18 USC 1519, which makes it a crime to alter, destroy, mutilate or conceal a document or tangible object “with the intent to impede, obstruct, or influence the investigation or proper administration of any matter within the jurisdiction of any department or agency.”

A key element in most obstruction cases is intent, because to bring such a charge, prosecutors have to be able to show that whatever actions were taken were done to try to hinder or block an investigation. In the Trump case, prosecutors and federal agents are trying to gather any evidence pointing to the motivation for Trump’s actions.

The Washington Post reported in October that Trump’s valet, Walt Nauta, had told investigators that he moved boxes at Mar-a-Lago at the former president’s instruction after the subpoena was issued. Smith’s team has video surveillance footage corroborating that account, The Post reported, and considers the evidence significant.

In addition, the people familiar with the investigation said, authorities have another category of evidence that they consider particularly helpful as they reconstruct events from last spring: emails and texts of Molly Michael, an assistant to the former president who followed him from the White House to Florida before she eventually left that job last year. Michael’s written communications have provided investigators with a detailed understanding of the day-to-day activity at Mar-a-Lago at critical moments, these people said.

Michael’s lawyer did not respond to requests for comment.

Investigators have also amassed evidence indicating that Trump told others to mislead government officials in early 2022, before the subpoena, when the National Archives and Records Administration was working with the Justice Department to try to recover a wide range of papers, many of them not classified, from Trump’s time as president, the people familiar with the investigation said. While such alleged conduct may not constitute a crime, it could serve as evidence of the former president’s intent.

These people said prosecutors have collected evidence that Trump ignored requests from multiple advisers to return the documents to the archives over a period of a year, that he asked advisers and lawyers to release false statements claiming he had returned all documents, and that he grew angry after being subpoenaed for the documents.

Investigators also have evidence that Trump sought advice from other lawyers and advisers on how he could keep documents after being told by some on his team that he could not, people familiar with the investigation said. They have collected evidence that multiple advisers warned Trump that trying to keep the documents could be legally perilous.

As investigators piece together what happened in May and June of last year, they have been asking witnesses if Trump showed classified documents, including maps, to political donors, people familiar with those conversations said.

Such alleged conduct could demonstrate Trump’s habits when it came to classified documents, and what may have motivated him to want to keep the papers. The Post has previously reported that Trump told aides he did not want to return documents and other items from his presidency – which by law are supposed to remain in government custody – because he believed they belonged to him.

President Donald Trump listens to Gen. Mark A. Milley, chairman of the Joint Chiefs of Staff, during a meeting of the White House coronavirus task force at the White House in April 2020. Jabin Botsford/The Washington Post

Investigators have also asked witnesses if Trump showed a particular interest in material relating to Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, people familiar with those interviews said. Milley was appointed by Trump but drew scorn and criticism from Trump and his supporters after a series of revelations in books about Milley’s efforts to rein in Trump toward the end of his term. In 2021, Trump repeatedly complained publicly about Milley, calling him an “idiot.”

The people did not say whether investigators specified what material related to Milley they were focused on. The Post could not determine what has led prosecutors to press some witnesses on those specific points or how relevant they may be to the overall picture that Smith’s team is trying to build of Trump’s actions and intent.

But people familiar with the matter stressed that a major thrust of the investigation has been the question of obstruction, and whether Trump sought to deliberately prevent officials from gathering all of the classified material at Mar-a-Lago.

The case stretches back to efforts by Archives officials to retrieve documents and other items from the former president in 2021, after they came to believe that some presidential records from the Trump administration – such as letters from North Korean leader Kim Jong Un – were unaccounted for, and perhaps in Trump’s possession.

After months of back-and-forth, Trump agreed in January to turn over 15 boxes of material. When archivists examined the material, they found 184 documents marked classified, including 25 marked top secret, which were scattered throughout the boxes in no particular order, according to court filings.

That discovery suggested to authorities that Trump had not turned over all the classified documents in his possession when he left the White House. In May, a grand jury subpoena demanded the return of classified documents with a wide variety of markings, including a category used for secrets about nuclear weapons.

In response to the subpoena, Trump’s advisers met with government agents and prosecutors at Mar-a-Lago in early June, handing over a sealed envelope containing another 38 classified documents, including 17 marked top secret, according to court papers. According to government filings, Trump’s representatives claimed at the meeting that a diligent search had been conducted for all classified documents at the club.

Agents continued to gather evidence that suggested Trump was not fully complying with either government requests or subpoena demands, and that his team might have misled authorities and possibly held onto some sensitive files.

On Aug. 8, FBI agents conducted a surprise court-ordered search of Mar-a-Lago and found 103 documents marked classified, including 18 marked top secret, according to court papers. The investigation has recovered documents that describe highly sensitive U.S. intelligence efforts aimed at China, one document describing Iran’s missile program and material covering other sensitive topics, including nuclear secrets.

Smith’s team has been presenting witnesses and evidence for months to a grand jury in Washington focused on the Mar-a-Lago probe, even as a separate grand jury at the same federal courthouse hears evidence related to efforts to block the results of the 2020 election, and the state-level prosecutors in New York and Georgia press forward with their cases.

The Mar-a-Lago prosecutors recently won a court fight that allowed them to question Trump’s lawyer, Evan Corcoran, before the grand jury about what he knew about the documents.

Grand jury proceedings are secret, and Smith has given no public indication of the pace of his investigation or when he expects it to be finished.