BATON ROUGE, La. (AP) — A federal grand jury has charged more than 20 people, including inmates and former guards, with smuggling drugs into the Louisiana State Penitentiary at Angola.

Documents unsealed Tuesday show five former guards and several inmates were among the 22 people indicted on conspiracy and drug trafficking charges following a federal and state investigation.

The investigation aimed to stop marijuana, cocaine and methamphetamines from being brought into the prison through the mail and by prison staff.

The Advocate reports authorities described the operation as "large-scale," and court documents listed four people arrested in California who're accused of shipping drugs to Louisiana.

U.S. Attorney Brandon J. Fremin said the seven Angola inmates who were indicted are currently serving lengthy sentences, including life.

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Information from: The Advocate, http://theadvocate.com