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.

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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.

A criminal defendant has a constitutional right not to be compelled to be a witness against himself, but there is no privilege to withhold or conceal preexisting evidence. In some cases, there is an issue whether the act of producing the evidence is itself testimonial and hence privileged. See United States v. Hubbell, 530 U.S. 27 (2000). That doesn't look like a big issue here.