Oakland's Oaksterdam University was taken over by federal officials Monday.
Officers wearing U.S. Marshals, IRS and DEA jackets swarmed the Oakland medical marijuana facility on Broadway before 8 a.m. Investigators put yellow crime tape around the entire building.
In all, at least four locations were sealed off by the feds.
Oaksterdam is considered by many as the heart of California's pot legalization movement.
Officials on the scene were not commenting on their purpose other than to say that it was part of "an ongoing investigation." Internal Revenue Service spokeswoman Arlette Lee said that the investigation was under seal in a Northern District Court.
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