He is charged with murder, armed robbery, kidnapping and other charges in connection with the death of Eve Carson back in 2008.
She had been shot five times with a 12-gauge shotgun. Her body was found in the middle of a street in a Chapel Hill neighborhood.
Atwater pleaded guilty last month to several charges, including carjacking resulting in death and kidnapping.
Atwater is scheduled to be sentenced in federal court Sept. 23.
His agreement with prosecutors is for a life sentence.
Laurence Lovette also faces state charges in the case.