NEW ORLEANS -- A whistleblower who exposed illegal dumping of oil and chemicals in the Gulf of Mexico in 2014 has filed a civil lawsuit against the U.S. government for allegedly letting the polluters off easy.

Evan Howington of Brazoria County, Texas, came to WWL-TV last year to expose the dumping incident and an apparent cover-up attempt, all of which he caught on video as a crew member on an offshore oil rig.

Howington recorded his supervisors on the Uncle John vessel opening a valve on a pipeline and releasing what appeared to be oil and chemicals into the Gulf for 90 minutes.

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The New Orleans-area U.S. Attorney’s Office used Howington’s video evidence to get a criminal conviction in the form of a plea deal with Walter Oil & Gas, the oil company that had hired the rig and its crew. Under the deal, Walter pleaded guilty to one count of failing to report a discharge and agreed to pay a $400,000 fine.

But, as WWL-TV reported last year in its series “Oil & Water,” the video Howington captured secretly with his cell phone clearly showed his bosses laughing about the discharge, acknowledging that it’s illegal, agreeing to say it wasn’t oil “if anybody asks” and discussing how to report it on official logs simply as “relieve pressure.”

Howington said that after meeting with government investigators and prosecutors in New Orleans, the lead prosecutor on the case changed. The lawsuit says the new prosecutor, John Maestri, never met with Howington to go over the evidence and struck a plea deal that was a “gross mischaracterization of the evidence (Howington) had presented of intentional illegal conduct.”

The lawsuit alleges Maestri negligently failed to recognize that the Uncle John rig is a ship that sails under its own power and failed to collect $12 million by not charging Walter under a statute to prevent willful pollution from ships. Also, Howington could have collected up to $6 million as a whistleblower under that statute, but was ineligible for any whistleblower reward under which Walter was charged.

What’s more, the suit alleges Maestri negligently failed to press any charges against Cal-Dive and Helix Offshore, contractors that employed some of the supervisors who opened the valve and tried to hide the discharge.

Howington already brought these claims to the U.S. Department of Justice for an administrative review. Former U.S. Attorney Kenneth Polite told WWL-TV last year that he stood by Maestri’s handling of the case and expected the Justice Department to deny Howington’s claim. Howington said the Justice Department took no action on his claim. After six months, he took that silence to be the final denial he needed to file the civil claim in federal district court in Houston.