A fifth inmate has died violently in a Mississippi prison this week, raising further questions about security as clashes between prisoners continue. Mississippi's outgoing prisons chief said Friday that at least some of the five killings of inmates since Sunday stem from gang violence, as guards struggle to maintain control of restive inmates.

"These are trying times for the Mississippi Department of Corrections," Commissioner Pelicia Hall said in a statement Friday, hours after an inmate was found stabbed to death in his cell at the Mississippi State Penitentiary at Parchman.

Denorris Howell, 36, was found before 3 a.m. in his cell, covered in blood with a neck wound, becoming the fifth to die since violence erupted Sunday with a stabbing at South Mississippi Correctional Institute in Leakesville.

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Prison leaders are calling the gang fights "major disturbances," but Burton calls what's going on at Parchman "gang-related riots."

Hall said investigators believe only four of the five deaths are gang-related. The department didn't immediately say which death was not. She said the department won't confirm the names of the gangs "for security purposes," but relatives of inmates who spoke to The Associated Press and other news outlets say there's an ongoing confrontation between the Vice Lords and Black Gangster Disciples.

It wouldn't be the first time that the two gangs have warred behind bars in Mississippi, with previous confrontations at Parchman and other prisons over the past 15 years. A 2015 survey found nearly 3,000 Black Gangster Disciple members and nearly 2,000 Vice Lords in prisons statewide.

All state prisons statewide remained locked down Friday, confining inmates to cells and blocking visitors.

Besides Howell, Terrandance Dobbins, 40, was killed Sunday at South Mississippi. Walter Gates, 25, was stabbed and several other inmates were injured Tuesday at Parchman during a fight that spread to multiple units of the sprawling prison. Then on Thursday, Gregory Emary, 26, was killed at the Chickasaw County Regional Correctional Facility, a county-run jail that holds state inmates. Also Thursday, 32-year-old Roosevelt Holliman was fatally stabbed at Parchman in a fracas that led to multiple injuries.

Corrections officials have refused so far to say how many people overall have been injured, or whether there have been other violent incidents in prisons.

Candice Dobbins, the sister of Terrandance Dobbins, said she's been told violence began spreading after her brother's death.

Mississippi's prison system has struggled to fill guard vacancies, with Hall saying it's difficult to attract people with salaries that start below $25,000 a year. Some guards end up bringing illegal drugs and cell phones into prisons. Criminal charges were filed in 2014 against 26 state correctional officers.

Some prisons, including South Mississippi, have areas where many prisoners are housed in bunks in one large room, instead of individual cells. This can lead to worsened security problems. South Mississippi, in Greene County, was locked down for almost all of 2019, in part because of guard shortages.