Sources close to the investigation tell Forbes that Transocean engineers had last checked the blowout preventer 10 days before the rig explosion, and that BP believes the device suffered a leak of hydraulic pressure, preventing it from being able to shut the well.

FORBES: Fingers Crossed: Will BP's Box Stop Oil Spill?

But advocates for preventing nuclear proliferation say it highlights the risk that terrorists could obtain enough fuel to build a nuclear device.

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