"BP had clear policies requiring preservation of evidence in this case and has undertaken substantial and ongoing efforts to preserve evidence," the statement said.
The FBI said in court papers that Mix repeatedly was notified by BP that instant messages and text messages needed to be preserved.
In public statements, the company professed optimism that the top kill would work, giving it a 60 to 70 percent chance of success.
On May 26, the day the top kill began, Mix estimated in a text to his supervisor that more than 15,000 barrels of oil per day were spilling — three times BP's public estimate of 5,000 barrels and an amount much greater than what BP said the top kill could probably handle.
At the end of the first day, Mix texted his supervisor: "Too much flow rate — over 15,000 and too large an orifice." Despite Mix's findings, BP continued to make public statements that the top kill was proceeding according to plan, prosecutors said. On May 29, the top kill was halted and BP announced its failure.
BP stock closed at $41.91 Tuesday, a drop of just 4 cents. Analysts said investors evidently recognized the charges involved just one, low-ranking employee and saw no hint yet of any kind of larger cover-up on BP's part.
The explosion aboard the Deepwater Horizon drilling rig killed 11 workers. More than 200 million gallons of crude oil leaked from the well off the Louisiana coast before it was capped.
Under the Clean Water Act, polluters can be fined $1,100 to $4,300 per barrel of spilled oil, with the higher amount imposed if the government can show the disaster was caused by gross negligence.
Tom Becker, a fisherman in Biloxi, Miss., and head of the Mississippi Charter Boat Captains Association, said he wasn't surprised by the allegations.
"I don't trust BP one bit. That's what I've thought all along. It's like, 'What are they trying to hide today?'" Becker said.
He said his mistrust of BP had led him to hold out and not settle legally with the company over damages. He said his business has not recovered and he has no fishing trips booked for July, August or September, his busiest months. He blames that on the lingering perception that the Gulf is ruined and on high gas prices.
"I just wish we could get over it quick, but I don't see it happening, even though BP wants to pay everybody off and get them to shut up," Becker said.
Alabama Attorney General Luther Strange said he was pleased "the Justice Department is focused on holding those with criminal culpability accountable."
Associated Press writers Kevin McGill in New Orleans; Ramit Plushnick-Masti in Houston; Holbrook Mohr in Jackson, Miss.; and Bob Johnson in Montgomery, Ala., contributed to this report.
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