To see if US Vice President Joe Biden donated any papers that might have been classified, the FBI conducted two searches at the University of Delaware within the past month.
CBS, the BBC's US partner, reported that investigators took multiple boxes from the college on two separate days.
Thousands of boxes of documents from Mr. Biden's time in the Senate are kept at the university, which he attended as a student.
Regarding his handling of sensitive information, Donald Trump is under investigation.
Recently, Mr. Biden's home in Delaware and the offices he used in Washington, DC, both revealed the presence of documents marked classified. During a search of his private residence in Wilmington last month, the FBI discovered some of the files.
The University of Delaware was searched at the end of January and the beginning of February, according to sources familiar with the investigation who spoke to CBS.
Although it didn't appear that the recovered material had any classified markings, the FBI is currently looking over the files, according to CBS.
Similar to earlier searches, Mr. Biden and his team gave their consent, so no warrant was required, according to NBC News.
Mr. Biden donated 1,850 boxes of documents to the college in 2012, but those documents have not been made public since then.
The University of Delaware, the US Department of Justice, and Mr. Biden's private attorney have not yet responded.
The Justice Department has designated Robert Hur as a special counsel to oversee the investigation into how Mr. Biden handled confidential documents.
Following claims from his aides that they had found classified documents during their own search, the former US Vice-President Mike Pence's home was also searched last week.
Numerous documents with classified markings were discovered by FBI agents carrying out a search warrant at the former president's Florida Mar-a-Lago estate last year, prompting the opening of a separate investigation.
