A federal judge in San Francisco is due to sentence five leaders of a California prison gang. The men have already pleaded guilty to drug dealing, extortion and murder across northern California.

What's unusual is that the gang leaders were already serving life sentences in one of America's most secure prisons when they ordered the crimes.

California has the country's biggest prison system and the largest and oldest prison gangs. Most are headquartered at one facility: Pelican Bay State Prison. Experts say these gangs control crime far outside prison walls and across the country. Reporter Michael Montgomery of American RadioWorks spent six months following inmates and staff at Pelican Bay.

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