The search follows a 13-hour, top-to-bottom review of his Wilmington, Del., home on Jan. 20, when agents located additional documents with classified markings and also took possession of some of his handwritten notes.

The president has been voluntarily allowing the Justice Department into his residences as investigators seek to determine how classified documents from Biden’s time as vice president and a senator wound up in his home and office. The probe followed the Nov. 2 discovery of documents with classified markings by Biden’s lawyers as they closed up an office at the Penn Biden Center, a think tank affiliated with the Ivy League school.

Documents were also found at his Wilmington home by his personal lawyers, who initiated a search after the Penn Biden Center documents were discovered. The FBI also searched the center in November following the initial discovery of documents there, a person familiar with the matter told the Associated Press on Tuesday.

“Under DOJ’s standard procedures, in the interests of operational security and integrity, it sought to do this work without advance public notice, and we agreed to cooperate,” said the statement from Biden’s lawyer, Bob Bauer. “The search today is a further step in a thorough and timely DOJ process we will continue to fully support and facilitate. We will have further information at the conclusion of today’s search.”

An FBI spokeswoman referred comment to the Justice Department. A spokesman there did not immediately return a message seeking comment.

The Biden documents probe is being handled by a special counsel, Robert Hur, the former top federal prosecutor in Baltimore. He is starting his work this week, inheriting a months-long investigation already undertaken by FBI agents and Justice Department prosecutors.

The Bidens purchased the home, which overlooks a state park adjacent to the beach, in June 2017, months after he left the vice presidency.