NEW ORLEANS - Now that BP appears to have vanquished its ruptured well, authorities are turning their attention to gathering evidence from what could amount to a crime scene at the bottom of the sea.

The wreckage - including the failed blowout preventer and the blackened, twisted remnants of the drilling platform - may be "Exhibit A" in the effort to establish who is responsible for the biggest peacetime oil spill in history. And the very companies under investigation will be in charge of recovering the evidence.

Hundreds of investigators can't wait to get their hands on evidence. The FBI is conducting a criminal investigation, the Coast Guard is seeking the cause of the blast, and lawyers are pursuing millions of dollars in damages for the families of the 11 workers killed, the dozens injured and the thousands whose livelihoods have been damaged.

"The items at the bottom of the sea are a big deal for everybody," said Stephen Herman, a New Orleans lawyer for injured rig workers and others.

BP will surely want a look at the items, particularly if it tries to shift responsibility for the disaster onto other companies, such as Transocean, which owned the oil platform, Halliburton, which supplied the crew that was cementing the well, and Cameron International, maker of the blowout preventer.

BP and Transocean - which could face heavy penalties if found to be at fault - have said they will raise some of the wreckage if it can be done without doing more damage to the oil well. That would give the two companies responsibility for gathering up the very evidence that could be used against them.

But the federal government has said it simply doesn't have the know-how and the deep-sea equipment that the drilling industry has. And it said the operation will be closely supervised by the Coast Guard.

Lawyers will be watching, too, to make sure the companies don't do anything untoward, said Brent Coon, an attorney for one of the thousands of plaintiffs seeking damages.

"I think they would do something in front of their own mother if they could," Coon said. "But the reality is there are a lot of eyes watching them and a lot of smart scientists who would know if they did anything they weren't supposed to."

The crisis in the Gulf appeared to be drawing to a close this week when BP plugged up the top of the blown-out well with mud and then sealed it with cement. BP Senior Vice President Kent Wells said crews plan to resume drilling Sunday night on a relief well more than two miles below the seafloor that will be used to inject mud and cement just above the source of the oil, thereby sealing off the well from the bottom, too. The two wells should hook up between Aug. 13 and Aug. 15, Wells said.

In other developments Friday, BP said it might drill again someday into the same undersea reservoir of oil, which is still believed to hold nearly $4 billion worth of crude. That prospect is unlikely to sit well with Gulf Coast residents furious at the oil giant.

"There's lots of oil and gas here," Chief Operating Officer Doug Suttles said. "We're going to have to think about what to do with that at some point."

Also Friday, BP said Suttles - who has spent more than three months managing BP's response efforts on the Gulf - is returning to his day job in Houston. Mike Utsler, a vice president who has been running BP's command post in Houma, La., since April, will replace him.

Willie Davis, a 41-year-old harbormaster in Pass Christian, Miss., said he fears his area will be forgotten if BP pulls out too soon. "I'm losing trust in the whole system," he said. "If they don't get up off their behinds and do something now, it's going to be years before we're back whole again."

Utsler told Gulf residents not to worry, saying the spill's effects are "a challenge that we continue to recognize with more than 20,000-plus people continuing to work."

Investigations of the disaster began immediately after the rig blew up on April 20. The government alone is conducting about a dozen, including several congressional investigations, criminal and civil probes by the Justice Department, and an examination by an expert panel convened by President Barack Obama.

Officials want to find out not only the cause of the explosion, but also how oil drilling a mile or more below the surface can be made safer.

A final outcome could be years away, particularly if someone is charged with a crime, said David Uhlmann, former chief of the Justice Department's environmental crimes team.

"Normally an investigation of a case this complicated would take two to three years. This is not a normal case," he said. "This is the worst environmental disaster in U.S. history. The timetable will be accelerated dramatically, but it still will not be resolved before 2011."

Any items brought up from the seafloor will be photographed and preserved. Investigators for the government, BP and others who have a stake in the case will try to come up with testing procedures acceptable to all sides.

The blowout preventer will probably make it to the surface. The 300-ton mechanism is designed to be placed on a well and brought back to the surface for reuse. It was supposed to be the final line of defense against a catastrophic spill, but BP documents obtained by a congressional committee showed the device had a significant hydraulic leak and a dead or low battery.

"That piece of equipment will tell us whether the blowout preventer had a design defect or whether it was mechanical or human error that caused this disaster," Herman said.

The blowout preventer is still attached to the broken wellhead but will be replaced as part of the effort to permanently secure the well, said retired Coast Guard Adm. Thad Allen, who is overseeing the spill response for the government.

"In some ways it's the smoking gun," said Eric Smith, associate director of the Tulane Energy Institute. "It's rich evidence. It still won't tell you exactly what happened at the bottom of the well ... but the fact is it didn't work - and everybody wants to know why."

Coon said the rig might contain "black boxes" that recorded critical data and control panels that could be removed to re-create conditions before the explosion.

Transocean has asked the government for permission to test the blowout preventer and hopes to see it raised it in September, company President Steven Newman said.

Getting to the exploded rig itself might be harder. It would be impractical to raise the entire structure because of its immensity, twice the size of a football field, Coast Guard Rear Adm. Paul Zukunft said. He would not say whether it would be possible to cut off vital pieces of the structure.

Contributing to this report were Associated Press writers Dina Cappiello in Washington; Jason Dearen, Greg Bluestein and Harry R. Weber in New Orleans; and Brian Skoloff in Pass Christian, Miss.