The FBI has searched the University of Delaware twice in the past month to see if US Vice President Joe Biden donated any papers that might have been classified.
According to CBS, the BBC's US partner, investigators took multiple boxes from the college on two different days.
Thousands of boxes of documents from Mr. Biden's time in the Senate are kept at his alma mater, the university.
A criminal investigation into Donald Trump's handling of sensitive information is ongoing.
Recent months have seen the discovery of classified documents at Mr. Biden's Delaware home and Washington, DC, offices. During a search of his private residence in Wilmington by the FBI last month, some of the files were found.
According to sources familiar with the investigation, the University of Delaware searches took place at the end of January and the start of February.
Although the recovered material did not appear to have any classified markings, the FBI is currently looking over the files, according to CBS.
According to NBC News, Mr. Biden and his team gave their consent, as they had in previous searches, so no warrant was required.
In 2012, Mr. Biden gave the college 1,850 boxes of documents; however, those documents have not been made public since that time.
The US Department of Justice, the University of Delaware, and Mr. Biden's personal attorney have not yet responded.
Robert Hur, a special counsel, has been chosen by the justice department to head the investigation into Mr. Biden's handling of sensitive documents.
The former US Vice-President Mike Pence's residence was also searched last week after his aides disclosed that they had found classified documents during their own search.
After FBI agents serving a search warrant at the former president's Florida Mar-a-Lago estate last year discovered hundreds of papers with classified markings, the former president is now the subject of a separate investigation.