Related video above: Mike Pence says he'll decide on presidential run over holidaysDocuments with classified markings were discovered in former Vice President Mike Pence's Indiana home last week, his lawyers says, the latest in a string of recoveries of confidential information from the homes of current and former top U.S. officials.The records "appear to be a small number of documents bearing classified markings that were inadvertently boxed and transported to the personal home of the former vice president at the end of the last administration," Pence's lawyer, Greg Jacob, wrote in a letter to the National Archives shared with The Associated Press.He said that Pence had been "unaware of the existence of sensitive or classified documents at his personal residence" until a search last week and "understands the high importance of protecting sensitive and classified information and stands ready and willing to cooperate fully with the National Archives and any appropriate inquiry."The revelation came as the Department of Justice was already investigating the discovery of documents with classification markings in President Joe Biden's home in Delaware and his former Washington office, as well as former President Donald Trump's Florida estate. Democrat Biden has indicated he will seek reelection, and Republican Pence has been exploring a possible 2024 presidential campaign that would put him direct competition against his former boss. The newest discovery thrusts Pence, who had previously insisted that he followed stringent protocols regarding classified documents, into the debate over the handling of secret materials by officials who have served in the highest ranks of government.Trump is currently under criminal investigation after roughly 300 documents with classified markings, including at the top-secret level, were discovered at Mar-a-Lago. Officials are trying to determine whether Trump or anyone else should be charged with illegal possession of those records or with trying to obstruct the months-long criminal investigation. Biden is also subject to a special counsel investigation after classified documents from his time as a senator and in the Obama administration were found at his properties.Trump, who denies any wrongdoing, reacted to the new development on his social media site: "Mike Pence is an innocent man. He never did anything knowingly dishonest in his life. Leave him alone!!!"While a very different case, the Pence development could either dilute or increase the attention on Trump and Biden, who have sought to downplay the importance of the discoveries at their homes. The presence of secret documents at all three men's homes further underscores the federal government's unwieldy system for storing and protecting the millions of classified documents it produces every year.Pence's lawyer, Jacob, said in his letter that the former vice president had "engaged outside counsel, with experience in handling classified documents" to review records stored at his home on Jan. 16 "out of an abundance of caution" after the Biden documents became public.Jacob said the Pence documents were immediately secured in a locked safe. According to a follow-up letter from the lawyer dated Jan. 22, FBI agents visited Pence's residence the night of Jan. 19 to collect the documents that had been secured. He was still in Washington at the time.A total of four boxes containing copies of administration papers —- two in which "a small number" of papers bearing classified markings were found, and two containing "courtesy copies of vice presidential papers" were discovered. Arrangements were made to deliver those boxes to the National Archives Monday.The National Archives did not immediately respond to a request for comment on the discovery, which was first reported by CNN.A Justice Department spokesman declined to comment Tuesday, and a lawyer for Pence did not immediately respond to an email seeking elaboration.Pence told the Associated Press in August that he did not take any classified information with him when he left office.Asked directly if he had retained any such information, he said, "No, not to my knowledge."In a January interview with Fox Business, Pence described a "very formal process" used by his office to handle classified information as well as the steps taken by his lawyers to ensure none was taken with him."Before we left the White House, the attorneys on my staff went through all the documents at both the White House and our offices there and at the vice president's residence to ensure that any documents that needed to be turned over to the National Archives, including classified documents, were turned over. So we went through a very careful process in that regard," Pence said.A spokesperson for former President Barack Obama referred to a 2022 statement from the National Archives that said the agency took control of all of Obama's records after he left office and "is not aware of any missing boxes of presidential records from the Obama administration"Freddy Ford, a spokesperson for former President George W. Bush, told AP that "all presidential records - classified and unclassified - were turned over to NARA upon leaving the White House."A spokesperson for Bill Clinton said all classified documents are in NARA custody and there have been no instances of any being found elsewhere since he left office in 2001.A spokesman said former Vice President Dick Cheney didn't leave office with classified materials and at no point since have any been discovered.Mike Pompeo, who served the Trump administration as secretary of state and is mulling his own 2024 GOP presidential bid, said during a stop in South Carolina in late August that the FBI search of Mar-a-Lago "was a deeply politicized use of the FBI."Asked by AP if he took any classified material with him after leaving the administration, Pompeo replied, "no," adding, "No one should have classified information out of the appropriate place for classified information, anytime, full stop, period."Public records show Pence and his wife, Karen, bought their seven bedroom, 10,300 square foot home in Carmel, Indiana, in May 2021 -- about four months after moving out of the vice president's residence in Washington. The Indiana property is spread over a five acre lot just north of Indianapolis.___Associated Press writers Eric Tucker and Zeke Miller contributed to this report from Washington.