Officials say Clark was attacked while taking two inmates to the food hall. Marko Willingham was the other inmate and he was also injured when trying to assist Officer Clark.
Officer Clark was pronounced dead upon arrival at the local hospital. Officer Clark had only worked at the prison since April.
Lester was already in prison for numerous crimes, including a murder in 2007, according to state jail records.
Willingham remains in the hospital with non-life-threatening injuries, according to the corrections department.
Lester is expected to be charged with the assault and resulting death of Clark, as well as the assault on Willingham.
“The entire [Georgia Department of Corrections] team is mourning the loss of one of our own and we collectively express our deepest condolences to Officer Clark’s family and friends,” GDC Commissioner Tyrone Oliver said in a statement. “We will support them as they navigate this tragedy over the coming days, weeks and months.”
Few more details were revealed about the deadly attack.