An appeals court in Louisiana said it granted a new trial for a former BP engineer, Kurt Mix, on grounds of jury exposure to external evidence.

Mix was charged with determining the amount of oil leaking from the Macondo well after Deepwater Horizon collapsed in 2010 as a result of a cascading series of failures beneath the rig. He was prosecuted and later convicted of obstruction of justice for deleting text messages and other correspondence related to those calculations.

The U.S. Court of Appeals for the Fifth Circuit said Mix's defense team charged that a jury in the case was exposed to evidence not presented at the trial.

"During a deadlock in deliberations, Juror 1 told the rest of the jury that she had overheard something that increased her confidence in voting guilty. Other members of the jury prevented her from revealing what she had overheard," the court's opinion read. "The district court ordered a new trial based on the jury's exposure to extrinsic evidence."

All but a handful of the deleted text messages eventually were recovered by forensic experts. His defense team argued most of the deleted messages were not germane to the spill, which showed there was no cover-up attempt.

Prosecutors, however, charged that Mix deliberately deleted messages related to BP executives' knowledge of how much oil was flowing from the failed Macondo well.

The U.S. District Court of the Eastern District of Louisiana ruled last year that BP released 3.2 million barrels of oil into the Gulf of Mexico in 2010, about 1 million barrels less than the government estimated.

The district court ruled in September that BP's activities at the Macondo well beneath the Deepwater Horizon rig in the Gulf of Mexico amounted to willful misconduct

Mix was the first person to be tried in the 2010 disaster, which left 11 rig workers dead.