A federal appeals court has ruled that investigators can review millions of documents seized by authorities last year from embattled businessman Jeffrey Thompson.

The U.S. Court of Appeals for the District of Columbia Circuit held in a sealed opinion on Tuesday that prosecutors could review the records as a part of their long-running probe of campaign finance practices in the city. The Washington Post first reported the ruling.

Thompson's lawyers sought last year to limit investigators' access to the records, arguing that some of them could be subject to legal protections like attorney-client privilege.

But federal authorities argued that they could put a system into place to curb the exposure of restricted information.

Thompson is a key figure in the investigation of D.C. Mayor Vincent Gray's 2010 campaign, and authorities searched his home and offices last March.

Although Thompson has not been charged with a family, people familiar with the probe have said he bankrolled a $653,800 shadow campaign to help elect Gray.

Last July, a longtime Thompson associate pleaded guilty to her role in the scheme.

Gray has denied wrongdoing and said he will not resign.