The man accused of slaying an Edison gas station clerk late last year killed his cellmate during a fight in his South Carolina jail cell, authorities said.

Marcus A. Wright, 22, of Beaufort, South Carolina, was arrested on Jan. 3 in his home state on charges of first-degree murder, first-degree armed robbery, second-degree conspiracy to commit armed robbery and a second-degree weapons offense in the December robbery of the Speedway gas station on Amboy Avenue in Edison.

After getting the cash, the robber fired a single shot, killing 38-year-old John Bertram, a resident of the Fords section of Woodbridge, Middlesex County prosecutors said.

Wright had not yet been extridicted to New Jersey to face charges for the Edison robbery.

The South Carolina Department of Corrections told WLTX-TV that Wright was charged with murder in the death of cellmate Matthew Williams at Lieber Correctional Institute in Dorchester County.

An earlier arrest booking photo of Marcus A. Wright (Middlesex County Prosecutor's Office)

According to the incident report, Wright hit Williams in the face and head with a "personal weapon" causing severe injuries to his face and head, WLTX reported.

The warrant says Williams died from blunt force trauma.

It's unclear when Wright will be extradited to New Jersey.

Wright has twice served time in the South Carolina jails for burglary. He finished serving his latest sentence for burglary and smuggling on Oct. 1. He was released to the Dorchester County Sheriff’s Department, where he remains in custody at the Dorchester County Detention Center as he faces the murder charge.

In the Edison case, Olya Quinnam, 22, was charged with second-degree conspiracy to commit armed robbery and hindering apprehension. Prosecutors said she waited outside the store during the robbery. She pleaded guilty on Sept. 26 to one count of first-degree armed robbery under a plea agreement with prosecutors and is scheduled to be sentenced to 15 years in prison on Nov. 8., according to the Middlesex County Prosecutor's Office.

Contact reporter Dan Alexander at Dan.Alexander@townsquaremedia.com or via Twitter @DanAlexanderNJ

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