Since November, after the discovery of documents with classified markings in his former office, Biden aides have been searching for any additional classified materials that might be in other locations he used, said the source, who spoke on the condition of anonymity to provide details about the ongoing inquiry.The search was described as exhaustive, with the goal of getting a full accounting of all classified documents that may have inadvertently been packed in boxes when Biden cleared out of the vice president’s office space in January 2017.U.S. Attorney General Merrick Garland has asked John R. Lausch, U.S. attorney for the Northern District of Illinois and a holdover Trump appointee, to review how the classified material ended up in the closet, a source familiar with the matter told NBC News on Monday.Trump's possession of over 100 documents with classified markings despite have been subpoenaed for their return is the subject of a federal criminal investigation by the Justice Department.Bradley Moss, a lawyer who specializes in national security issues and a frequent Trump critic, tweeted after the NBC report: "Nothing I have seen has changed my mind yet that Biden and his team, for now at least, are not at risk of criminal exposure."