Former BP engineer Kurt Mix, the first defendant in a criminal case over the 2010 Gulf of Mexico oil spill, has faced jurors in New Orleans over claims that he destroyed evidence.
Mix, who helped lead efforts to cap BP's deep-water Macondo well off the coast of Louisiana, was charged with destroying evidence that US proescutors had demanded to see as part of their investigations into the largest oil spil of the US coastline in its history.
Federal prosecutor Jennifer Saulino told jurors that Mix deleted 513 text messages and three voicemails about the estimated size of the spill.
Mix knew that BP's internal estimates of the flow rate from the well were "well above" the numbers the company was citing publicly and the maximum 15,000 barrel-a-day limit for the Top Kill capping operation to be successful, prosecutors said.
They said that Mix did not divulge the information at a meeting between government officials and BP engineers in May 2010 and erased references to it on his iPhone.
Mix, charged in 2012 with two counts of obstruction of justice, has pleaded not guilty.
"This is a case about a BP engineer, Kurt Mix, who in the wake of the massive Macondo oil spill, was told over and over not to delete messages, and he made the choice to do it anyway," Saulino told jurors.
"Mr Mix was not some low-level guy. The evidence will show that he was, internally, the go-to guy on flow rate for BP," Saulino added.
But Mix's lawyer Joan McPhee maintained that Mix did not have the level of importance that Saulino claimed. "He was a first responder just like a firefighter who shows up when the house is already on fire," said McPhee.
Mix "repeatedly shared with the government, all through the Macondo response effort, the very same information that prosecutors claim he was trying to hide," McPhee added.
Mix deleted some messages, she said. "There is no dispute about that. But that is not the issue in this case.
"He wasn't intending to hide anything. He had nothing to hide because he had done nothing wrong," she added.
The oil spill set off a federal investigation and resulted in thousands of lawsuits against BP, Transocean and Halliburton.
Transocean owned the Deepwater Horizon drilling rig that burned down and sank, while Halliburton provided cement services for the well.
Three other BP employees were charged with crimes relating to the spill charges after Mix was arrested. All three pleaded not guilty.
David Rainey, the company's former vice-president of exploration for the Gulf of Mexico, goes to trial in March.
Robert Kaluza and Donald Vidrine face trial in June.
Halliburton agreed in July to plead guilty to a misdemeanor for failing to preserve computer models of the final cement job that capped the well. The company paid a statutory maximum fine of $200,000.
Transocean pleaded guilty in February to violating the US Clean Water Act and agreed to pay a $400m fine.
BP pleaded guilty to 14 criminal counts and agreed in 2012 to pay $4bn to resolve the federal criminal probe of its role in the spill.