Federal agents seized more than 60 boxes of documents and electronic copies of more than 20 million pages of records in their investigation of a powerful D.C. business executive, according to a recently unsealed court opinion.

In a ruling made public May 25, U.S. District Judge Royce C. Lamberth disclosed that prosecutors had not yet inspected any of the records seized in March from the home and offices of Jeffrey Thompson, a self-made businessman and philanthropist.

Thompson was chairman of D.C. Chartered Health Plan, a managed care firm that, with a $322 million annual contract, is the city’s single largest vendor.

Federal authorities have refused to discuss the investigation into Thompson, which is believed to be focusing on campaign donations and his dealings with city officials and council members.

Thompson’s attorney, Brendan Sullivan, declined to comment.

The haul of records became public when Lamberth ruled on a request by the businessman’s lawyers to limit the scope of records that authorities can review. The opinion, which was first reported by Mike Scarcella of the Legal Times, does not identify Thompson, but it is clear from the ruling that Lamberth is referring to that investigation.

Some of those records collected by investigators are protected by various privileges, including the attorney-client privilege, Lamberth wrote. To prevent prosecutors from being exposed to such records, the District’s U.S. Attorney's Office set up a ”filter team” unconnected with the investigation to review documents that might contained privileged information.

That team will then submit those records to Thompson’s lawyers for review. The defense attorneys may then raise objections with a judge in the hopes of stopping the case’s prosecutors from seeing them.

Thompson’s attorneys filed court papers to block that process, arguing that they alone should be permitted to first inspect such records, Lamberth wrote.

Lamberth ruled in favor of prosecutors, writing that “the Court has no reason to doubt the good faith of the government or its willingness to abide by the procedures it has suggested. Those procedures will ensure that the investigation team has no access to potentially privileged documents.”

The judge added that it was in prosecutors’ best interest to follow such rules because “any leaks between the filter team and the investigation team — or, if an indictment issues, the prosecution team — may lead to a violation of” Thompson’s Constitutional rights and “compromise the prosecution’s ability to secure a conviction.”

The investigation of Thompson is just one of many involving potential corruption in city government. Two of Mayor Vincent Gray’s 2010 campaign workers pleaded guilty last month to scheming to divert campaign funds to a minor mayoral candidate. Their goal was to keep that candidate in the race to attack incumbent Mayor Adrian Fenty. Gray went on to beat Fenty in the Democratic primary and then cruised to a general election victory.

City Council member Harry Thomas (D) was recently sentenced to 38 months in federal prison for stealing $350,000 from city taxpayers. And City Council chairman Kwame Brown (D) is being investigated by federal authorities for potential misdeeds related to his 2008 campaign and other matters.

Read more: The Post’s criminal justice coverage | D.C. politics coverage