In May of last year, shortly after the Justice Department issued a subpoena to former President Donald Trump for all classified documents at his Mar-a-Lago estate, Trump's then-lead attorney on the matter, Evan Corcoran, warned the former president in person, at Mar-a-Lago, that not only did Trump have to fully comply with the subpoena, but that the FBI might search the estate if he didn't, according to Corcoran's audio notes following the conversation.

Only minutes later, during a pool-side chat away from Trump, Corcoran got his own warning from another Trump attorney: If you push Trump to comply with the subpoena, "he's just going to go ballistic," Corcoran recalled.

Corcoran's recollections, captured in a series of voice memos he made on his phone the next day, help illuminate Trump's alleged efforts to defy a federal grand jury subpoena, and appear to shed more light on his frame of mind when he allegedly launched what prosecutors say was a criminal conspiracy to hide classified documents from both the FBI and Corcoran, his own attorney.

Trump has pleaded not guilty to all charges against him and has denied any wrongdoing.

The recordings, which have become a key piece of evidence in special counsel Jack Smith's classified documents case against Trump, contain information that was later described in Smith's publicly released indictment and in media reports -- but many of the details in them have never been made public.

ABC News has reviewed copies of transcripts of the recordings, which appear to show the way Trump allegedly deceived his own attorney, and how classified documents, according to prosecutors, ended up at Mar-a-Lago in the first place.

Trump campaign spokesperson Steven Cheung, responding to the development, told ABC News, "The attorney-client privilege is one of the oldest and most fundamental principles in our legal system, and its primary purpose is to promote the rule of law. Whether attorneys' notes are detailed or not makes no difference -- these notes reflect the legal opinions and thoughts of the lawyer, not the client."

Cheung added that Trump "offered full cooperation with DOJ, and told the key DOJ official, in person, 'Anything you need from us, just let us know.'"

A spokesperson for the special counsel's office declined to comment to ABC News. Corcoran did not immediately return ABC News' request for comment.

'Complying with that subpoena'

When Corcoran joined Trump's legal team in April last year, the FBI had already launched a criminal investigation into Trump's handling of classified information. Nearly 200 classified documents had been found in 15 boxes that Trump reluctantly returned to the National Archives "after months of demands," as the indictment stated.

But Justice Department officials believed Trump was holding onto even more classified documents in other boxes at Mar-a-Lago and refusing to return them -- so on May 11, 2022, the Justice Department issued a federal grand jury subpoena demanding the return of any and all classified documents.

Corcoran and another Trump attorney, Jennifer Little, flew to Florida to meet with Trump. "The next step was to speak with the former president about complying with that subpoena," Corcoran recalled in a voice memo the next day.

But while sitting together in Trump's office, in front of a Norman Rockwell-style painting depicting Ronald Reagan, Gerald Ford, Bill Clinton and Trump playing poker, Trump, according to Corcoran's notes, wanted to discuss something else first: how he was being unfairly targeted.

As Corcoran later recalled in his recordings, Trump continuously wandered off to topics unrelated to the subpoena -- Hillary Clinton, "the great things" he's done for the country, and his big lead in the polls in the run-up to the 2024 Republican presidential primary race that Trump would officially join in November. But Corcoran and Little "kept returning to the boxes," according to the transcripts.

Corcoran wanted Trump to understand "we were there to discuss responding to the subpoena," Corcoran said in the memos.

The FBI 'could arrive here'

As Corcoran described it in his recordings, he explained to Trump during that meeting what the former president was facing. "We've got a grand jury subpoena and the alternative is if you don't comply with the grand jury subpoena you could be held in contempt," Corcoran recalled telling Trump.

Trump responded with a line included in the indictment against him, asking, "what happens if we just don't respond at all or don't play ball with them?"

The transcripts reviewed by ABC News reveal what Corcoran says he then told Trump. "Well, there's a prospect that they could go to a judge and get a search warrant, and that they could arrive here," Corcoran recalled warning the former president as they sat at Mar-a-Lago.

Still, as depicted in Corcoran's recordings and in the public indictment, Trump repeatedly suggested it might be better if they refused to cooperate.

The indictment says that although Corcoran -- who ABC News believes to be "Attorney 1" in the indictment -- and Little -- believed to be "Attorney 2" -- "told Trump that they needed to search for documents that would be responsive to the subpoena and provide a certification that there had been compliance with the subpoena," Trump still insisted to them, "I don't want anybody looking through my boxes," and, "Wouldn't it be better if we just told them we don't have anything here?"

And in a private, pool-side conversation during a break at Mar-a-Lago that day, according to Corcoran's recordings, Little relayed to him what she was told herself by two other Trump attorneys: that Trump would "go ballistic" over complying with the subpoena -- "that there's no way he's going to agree to anything, and that he was going to deny that there were any more boxes at all," Corcoran recalled on his recordings.

In the indictment, prosecutors allege Trump did something just like that.

The indictment describes how, before the May 23 meeting with Corcoran at Mar-a-Lago ended, Trump "confirmed" a plan for Corcoran to return to Mar-a-Lago two weeks later to search for any classified documents. And, according to the indictment, Corcoran "made it clear to Trump" that he would conduct that search in a basement storage room.

Corcoran's recordings suggest he was told by others that the only location at Mar-a-Lago that contained classified documents was the basement storage room. "I've got boxes in my basement that I really wouldn't want you to go through," Corcoran recalled Trump telling him.

And sources told ABC News that, when speaking to investigators, Corcoran explained that he checked with many people about where classified documents could be found, and everyone, including Trump, created the impression that any classified documents would be in the boxes in the storage room.

A 'shocking break-in'

Over the next two weeks, before Corcoran returned to Mar-a-Lago to search for classified documents in the storage room, Trump's two co-defendants in the documents case, Mar-a-Lago staffers Walt Nauta and Carlos De Oliveira, allegedly removed dozens of boxes from the storage room -- all "at Trump's direction" and with the goal "that many boxes were not searched and many documents responsive to the May 11 Subpoena could not be found," according to the indictment.

Corcoran ultimately found 38 classified documents in the boxes that remained in the storage room, and he handed them over to the FBI, along with a certification -- allegedly endorsed by Trump -- that the former president had now fully complied with the subpoena.

But when FBI agents searched Mar-a-Lago three months later, they found 102 more classified documents in Trump's office and elsewhere.

Despite Corcoran warning him months earlier, according to the recordings, that the FBI might show up at Mar-a-Lago if he didn't fully comply with the subpoena, Trump called the FBI move a "shocking BREAK-IN," with "no way to justify" it, in posts on his social media platform.

According to the indictment, Trump "knowingly" deceived the FBI and his own attorney, providing "just some of the documents called for by the grand jury subpoena, while claiming that he was cooperating fully."

'Should be declassified'

The transcripts of Corcoran's recordings also appear to offer new insight into how classified documents ended up in boxes at Mar-a-Lago in the first place, and whether Trump truly believed those documents had been declassified.

As Trump described it to Corcoran according to the transcripts, he had a nightly practice while still in the White House: He would bring newspaper articles, photos and notes to his bedroom so he could review them.

He would also bring classified documents, according to Corcoran.

"That's the only time I could read something, and I had to read them so I could be ready for calls or meetings the next day," Trump told Corcoran, according to Corcoran's recordings.

However, in their meeting, Trump insisted to Corcoran that he made clear to those around him that "anything that comes into the residence should be declassified," the transcript reads.

"I don't know what was done," Corcoran recalled Trump telling him. "I don't know how they were marked. But that was my position."

Those comments from Trump, as recalled by Corcoran, suggest Trump understood that -- despite subsequent public claims to the contrary -- classified documents were not declassified simply by bringing them to the residence.

As for how classified documents ended up in boxes, Trump "had a lot of boxes" in his bedroom, and when he was done reading a newspaper article or a classified document, he'd "throw them" into one of the boxes, according to Corcoran.

So when it came time for Trump to leave the White House in January 2021, many of those boxes from the bedroom ended up at Mar-a-Lago in the storage room.

Corcoran provided special counsel Smith's team with his recordings after, as previously reported by ABC News, the now-former chief judge of the federal court in Washington ordered him to do so, finding that Smith's office had made a "prima facie showing that the former president had committed criminal violations" by deliberately misleading his attorneys about his handling of classified materials, sources familiar with the matter said at the time.

As a result of that legal fight, Corcoran recused himself from continuing to represent Trump in the documents case. But when Trump was arraigned in Washington on federal charges accusing him of trying to overturn the 2020 presidential election, Corcoran attended the hearing and sat in the courtroom behind Trump.