The US government said last night it is opening criminal and civil investigations into the country's worst oil spill.
The announcement by Attorney General Eric Holder came as President Barack Obama said that if any laws were broken in the Gulf of Mexico oil spill, people would be prosecuted.
Holder announced the criminal probe, though he would not specify the companies or individuals that might be targeted.
"We will closely examine the actions of those involved in the spill. If we find evidence of illegal behaviour, we will be extremely forceful in our response," Holder said in New Orleans.
President Obama was speaking at the White House as he ordered leaders of an independent commission investigating the spill "to follow the facts wherever they lead, without fear or favour."
He said their task was: "To thoroughly examine the spill and its causes, so that we never face such a catastrophe again."
Holder met the attorneys general of Louisiana, Alabama and Mississippi and several US attorneys. He said several senators have asked the Justice Department to determine whether criminal or civil laws were broken in the spill.
The Justice Department has told Senator Barbara Boxer, who heads the Senate's environment committee, that it has ordered BP, which leases the destroyed oil rig, not to destroy documents that could be relevant to investigators.
With the ambitious "top kill" abandoned over the weekend, BP's hope to staunch the leak lies with two relief wells that won't be finished until at least August.
The company is, however, trying another risky temporary fix to contain the oil and siphon it to the surface by sawing through the leaking pipe and putting a cap over the spill.
Coast Guard chief Thad Allen, the national incident commander, said today that BP was making its first major cut with super shears that weigh 46,000 pounds and resemble a giant garden tool. The company will also use a powerful diamond-edged cutter to try to make a clean cut above the blowout preventer, then will lower a cap over it with a rubber seal.
After several failed attempts to divert or block the well, BP's latest attempt involves cutting the broken riser pipe, making it spew as much as 20 % more oil into the water for days while engineers try to position a cap over the opening.
Eric Smith, an associate director of the Tulane Energy Institute, said the strategy had about a 50 to 70 % chance to succeed. He likened it to trying to place a tiny cap on a fire hydrant.
BP Chief Operating Officer Doug Suttles said there was no guarantee the cut-and-cap effort would work. He did say the company has learned from past efforts to contain the leak, which gives them a better shot at success.
"I'm very hopeful," Suttles said. "I think we'll find out over the next couple of days."