John Freeman, former sales VP of Pilot Flying J, pleaded guilty alongside three other former Pilot employees of mail fraud and wire fraud, making millions of dollars through fraudulent diesel rebates, reports the Knoxville News Sentinel.

The other individuals who plead guilty include former Pilot Regional Sales Manager John Spiewak, former Pilot Director of Inside Sales Vicki Borden, and former Regional Sales Representative Katy Bibee, according to the Knoxville News Sentinel.

Freeman came up with the plan to give trucking customers one diesel rebate, while surruptitiously charging them a different price, according to published reports. Spiewak oversaw the rebate contracts, while Borden monitored profits from the fraudulent rebates. Bibee negotiated the rebates with customers, the Knoxville News Sentinel reports. An investigation by the FBI and the Internal Revenue Service found that the plan to commit fraud began as early as 2008, and possibly earlier.

In October, former President Mark Hazelwood, former VP of National Sales Scott Wombold, and former regional sales representatives Heather Jones and Karen Mann will stand trial in Chatanooga, Tennessee. The guilty pleas open the possibility of Freeman, Spiewak, Borden, and Bibee testifying at October's trial, alongside 10 other former employees who also pleaded guilty, according to the Knoxville News Sentinel.

The FBI found that Pilot defrauded 5,500 customers of over $56 million. Pilot reached a settlement with authorities and customers in 2014 for $92 million and $87 million, respectively.