Notebooks President Biden used during his time as vice president that may reference classified information were among the material seized by the FBI during a search of his Delaware home last week, according to a report.

The notebooks include some of the 80-year-old president’s writings related to his official White House business, such as notes on diplomatic engagements during his time as Barack Obama’s vice president, according to NBC News.

While the notebooks themselves did not have classified markings, according to the report, some of Biden’s handwritten notes inside them may reference sensitive material.

A person familiar with the investigation told the news outlet that the president had a “large” collection of notebooks with handwritten notes on both personal and official subject matter, including his family life and his experiences or thoughts as vice president.