The estate of a state inmate who was killed during a prison melee has filed a lawsuit against the privately-run prison's management company and an unidentified inmate.

The Tulsa World (http://bit.ly/2cp7gSS ) reports that Kyle Tiffee's estate filed the lawsuit Tuesday. Four inmates were fatally stabbed and several other inmates were wounded during a September 2015 fight at the Cimarron Correctional Facility in Cushing, Oklahoma.

An Oklahoma prison workers group has said the deaths were the result of violence between two white gangs. The facility's management company, Tennessee-based Corrections Corp. of America, hasn't confirmed a motive for the stabbings.

The lawsuit alleges the company was negligent, and that prison staff were complicit in allowing contraband to be collected in inmates' cells and encouraged competition in drug trafficking that increased tension in the unit.

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Information from: Tulsa World, http://www.tulsaworld.com