A piece of the ruptured pipeline from last month's fatal accident in San Bruno, Calif., displayed in a laboratory at the National Transportation Safety Board's training center in Ashburn, Va. A preliminary NTSB report says a power failure led to a brief change in pipeline pressure but does not say that the pressure change caused the blast that killed eight people and destroyed 37 homes. Luis Alvarez/AP hide caption

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A worker with the Downtown Oakland Association sweeps the sidewalk near graffiti painted by protesters outside a drug store in Oakland on Friday. The federal government said it will investigate now that officer Johannes Mehserle was convicted Thursday of involuntary manslaughter, touching off angry protests that damaged stores and netted dozens of arrests. Eric Risberg/AP hide caption

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Richard Lee has created a multimillion-dollar empire in Oakland, Calif., built largely on medicinal pot. And now, he wants to take it a step further, by turning marijuana into a totally legal, taxable commodity for any Californian age 21 or older. Jeff Chiu/AP hide caption

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