Story highlights Mari Johnson is found unresponsive at the French Robertson Unit near Abilene

The Texas Department of Criminal Justice said the death is being investigated as a homicide

(CNN) A female correctional officer was killed by an inmate at a men's prison in Texas, Gov. Greg Abbott said Saturday.

Mari Johnson, 55, was found unresponsive in the kitchen area of the French Robertson Unit, a maximum security prison near Abilene, about 3 a.m. Saturday, Texas Department of Criminal Justice public information officer Robert Hurst said.

She was taken to a local hospital and pronounced dead, he said.

"The state of Texas mourns for Mari Johnson, a correctional officer who was senselessly murdered last night by an inmate," Abbott said in a news release. "Texas will ensure the perpetrator receives swift justice, and TDCJ has been instructed to take all necessary measures to enhance the safety of their staff to prevent such tragedies."

The TDCJ said the death is being investigated as a homicide, but didn't say who killed Johnson. Neither the governor nor TDCJ named a suspect.

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