He continued to contrast the discovery of sensitive materials in his own possession with the FBI seizure of documents at former President Donald Trump’s Florida estate in August.

“The best of my knowledge, the kind of things they [investigators] picked up are things that — from 1974, stray papers. There may be something else, I don’t know,” Biden said of the investigators that looked for materials in his possession. 1974 was Biden’s second year in the U.S. Senate, and he didn’t explain what type of material from that year he might have had in his possession.

He also maintained he “volunteered to open every single aperture” in cooperating with the Justice Department, a notable difference from Trump. The former president is under investigation not only for allegedly holding highly sensitive national security documents at his Mar-a-Lago estate, but also for possibly obstructing the investigation process. Trump has repeatedly complained about the process that led to the FBI seizures at Mar-a-Lago.

Classified documents have been found at Biden’s Wilmington, Del., home, as well as a Biden-associated private think tank space in Washington. Biden previously said he was “surprised” at the discovery of classified materials in the think tank space and that he didn’t know what was in them.

Federal agents also searched Biden’s Rehoboth Beach, Del., home last week, but no additional documents with classified markings were found, according to Biden’s personal lawyer.

His administration has repeatedly said they’re cooperating with the investigation, which is being led by special counsel Robert Hur.