Epstein is believed to have killed himself early Saturday at the Metropolitan Correctional Center in New York, where he was awaiting trial in a sex trafficking case.
Surveillance video reviewed after the death showed guards never made some of the checks noted in the log, according to the person familiar with the investigation.
The person wasn't authorized to disclose information and spoke to The Associated Press Tuesday on condition of anonymity.
The Justice Department said earlier Tuesday that two guards assigned to watch Epstein had been placed on administrative leave.