The FBI searched the University of Delaware in recent weeks for classified documents as part of its investigation into the potential mishandling of sensitive government records by Joe Biden.

The search, first reported by CNN, was confirmed to the Associated Press by a person familiar with the matter who was not authorized to discuss it publicly and spoke on condition of anonymity. The person would not say whether anything was found.

A justice department special counsel is investigating how classified documents from Biden’s time as vice-president and senator came to end up in his home and former office – and whether any mishandling involved criminal intent or was unintentional. Biden’s personal lawyers disclosed in January that a small batch of documents with classified markings had been found weeks earlier in his former Washington office, and they have since allowed FBI searches of multiple properties.

The university is Biden’s alma mater. In 2011, Biden donated his records from his 36 years serving in the US Senate to the school. The documents arrived on 6 June 2012, according to the university, which released photos of the numbered boxes being unloaded at the university alongside blue and gold balloons.

Under the terms of Biden’s gift, the records are to remain sealed until two years after he retires from public life.

Biden’s Senate records would not be covered by the Presidential Records Act, though prohibitions on mishandling classified information would still apply.

The White House referred questions to the justice department, which declined to comment. The University of Delaware also referred questions to the justice department.

The university is the fourth known entity to be searched by the FBI following inspections of Biden’s former office at the Penn Biden Center in Washington DC, where records with classified markings were initially found in a locked closet by Biden’s personal lawyers in November, and more recently of his Delaware homes in Wilmington and Rehoboth Beach.

Those searches were all done voluntarily and with the consent of Biden’s legal team.

The FBI took six items that contained documents with classified markings during its January search of the Wilmington home, Biden’s personal lawyer said. Agents did not find classified documents at the Rehoboth Beach property but did take some handwritten notes and other materials relating to Biden’s time as vice-president for review.

The justice department is separately investigating the retention by former president Donald Trump of roughly 300 documents marked as classified at his Florida estate, Mar-a-Lago. The FBI served a search warrant at the home last August after months of resistance by Trump and his representatives to returning the documents to the government.

The FBI also searched the Indiana home of former vice-president Mike Pence last week after his lawyers came forward to say they had found a small number of documents with classified markings. A Pence adviser said one additional document with classified markings was found during that search.