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.
The company's stock dropped 15 percent on the next trading day, the government said.
David Uhlmann, a University of Michigan law professor who was chief of the Justice Department's environmental crimes section, said the charges are probably "just the first of what will be multiple criminal charges."
"It could be the sign that the government believes there was a more far-reaching cover-up about the size of the spill," he said.
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.
Al Sunseri, whose family-owned oyster business was damaged by the spill, said there was little real news in the arrest of Mix. "I personally believe it's so involved that we could never really understand the magnitude of the bad players involved," he said.
Billy Nungesser, president of hard-hit Plaquemines Parish who has long accused BP of misleading the public about the spill, said: "We're just glad that the truth, and all the truth, will come out. Where crimes were committed, BP needs to pay the price."
Associated Press reporters Kevin McGill in New Orleans and Ramit Masti-Plushnick in Houston contributed to this story.
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