Authorities said Wilbourn shot and killed Memphis Police Officer Sean Bolton while Bolton tried to detain him in August 2015.
Prosecutors said Wilbourn used a gun while committing a carjacking as he tried to escape after the shooting. He pleaded guilty in April to carjacking, possessing a firearm during and in relation to the carjacking, and felony possession of ammunition.
Wilbourn pleaded guilty to the three charges under a deal with prosecutors that allowed him to avoid a federal trial. He still faces a first-degree murder charge in state court. State prosecutors said they will seek the death penalty if he is convicted. No trial date has been set.