Cooper is accused of killing five people to cover up a series of robberies throughout the Triangle. If convicted, he could face the death penalty.
Both sides agree Cooper shot and killed the five men in 2006 and 2007.
But defense attorneys argued that years of physical and emotional abuse by Cooper's father left him with diminished mental capacity and unable to plan the killings.
Prosecutors described Cooper as a cold-blooded serial robber who killed people to prevent them from identifying him.
The jury could begin deliberating as soon as Monday afternoon.