NEW ORLEANS (AP) — A federal judge has refused to throw out one of two obstruction of justice charges an ex-engineer for energy company BP faces after the 2010 Gulf of Mexico oil spill.

Kurt Mix is accused of deleting text messages about BP PLC’s response to the disaster.

Prosecutors claim Mix deliberately deleted more than 200 text messages to and from a supervisor and more than 100 others to and from a contractor to prevent them from being used in a grand jury probe of what Attorney General Eric Holder has called the largest environmental disaster in U.S. history.

Mix, of Katy, Texas, pleaded not guilty on May 3 to both counts. Each count is punishable by up to 20 years in prison and a $250,000 fine. To date, he is the only BP employee indicted in connection with the spill.

Defense lawyers said Thursday that the second of the two charges should be dismissed because it dealt with texts that amounted to innocuous messages among friends, most of them having little or nothing to do with work on the spill that resulted from the April 2010 explosion of the Deepwater Horizon drilling rig.

“It is not a crime, your honor, to delete inconsequential banter between friends and colleagues,” defense lawyer Joan McPhee told U.S. District Judge Stanwood Duval.

Duval agreed most of the texts were innocuous but he said some dealt with the spill. He said a jury would have to decide their relevance.

During a three-hour hearing on various defense and prosecution motions, Duval also turned down a defense motion seeking more details from the prosecution on how Mix is alleged to have impeded a grand jury investigation into the spill and response.

The judge declined to rule immediately on a defense motion seeking an array of documents dealing with BP’s measure of the flow from the spewing well and efforts to stop the flow.