OKLAHOMA CITY — Federal authorities sought this week to drop a criminal indictment of bid rigging against Oklahoma energy tycoon Aubrey McClendon, who died in a fiery single-car crash just hours after the indictment was announced.

Meanwhile, attorneys for a northwest Oklahoma landowner filed a class-action lawsuit Thursday against McClendon’s former company, Chesapeake Energy, alleging a conspiracy that involved another energy executive, ex-Sandridge Energy CEO Tom Ward.

The U.S. Department of Justice’s Chicago-based antitrust division alleged in the indictment against McClendon that he and unnamed co-conspirators orchestrated the conspiracy to rig bids for landowner leases in northwest Oklahoma. Ward, a longtime friend of McClendon’s who co-founded Chesapeake in the 1980s, was the CEO of Sandridge at the time the conspiracy was alleged to have occurred.

Justice Department spokesman Mark Abueg declined Thursday to confirm that Ward and Sandridge are the unindicted co-conspirators or that its investigation into the conspiracy is ongoing. Messages seeking comment Thursday from Ward and Sandridge were not immediately returned.

But Warren Burns, one of the attorneys who filed the class-action lawsuit, said it appears Ward and Sandridge Energy are the unindicted co-conspirators listed in the indictment against McClendon.

“Based on a number things, we think they are likely the unindicted co-conspirators,” Burns said.

Sandridge previously disclosed in filings with the U.S. Securities and Exchange Commission that it was the subject of a grand jury investigation into violations of federal antitrust law and that it is cooperating with federal investigators.

Chesapeake also has said it is cooperating with investigators.

Ward was ousted from Oklahoma City-based Sandridge in 2013 after a monthslong proxy fight and later formed his own company, Tapstone Energy LLC.

Ward and McClendon co-founded the natural gas giant Chesapeake Energy in 1989 with a handshake deal and an initial $50,000 investment and helped grow the company into one of the nation’s largest independent producers of natural gas in the United States.

McClendon also was a part-owner of the NBA’s Oklahoma City Thunder.

State officials say investigations into McClendon’s death could take months to complete. Oklahoma City police Sgt. Ashley Peters said a probe of Wednesday’s crash likely will take up to two weeks, while the state medical examiner’s office says an autopsy investigation could take as long as three months.