TULSA, Okla. (AP) — An Oklahoma man already serving life in prison on a murder charge has been sentenced to an additional 20 years of punishment for running a drug ring from behind bars.

Court records show 36-year-old Slint Kenneth Tate was sentenced Tuesday in U.S. District Court in Tulsa after pleading guilty in June to conspiracy to possess with intent to distribute methamphetamine.

Tate admitted in a plea agreement that he used cellphones smuggled to him in prison to run the drug operation.

Six co-defendants previously pleaded guilty to charges in the case.

Tate is already serving life-wit...