The coroner says based the entry wounds, the shooter was on higher ground than Ellis, shooting down into the off-duty officer.
Officials say there was debris on the on-ramp, and that when Ellis got out of his cruiser to clear the debris the suspect opened fire.
The coroner says Ellis was dead by the time first responders arrived at the scene.
State Police were originally notified of what appeared to be a fatal accident at the on-ramp off of the Bluegrass Parkway a few minutes before 3am on Saturday morning.
When a trooper arrived at the scene, they say they found Ellis still in uniform, near his cruiser.
Police say he had just gotten off work and was heading to his home in Bloomfield.
Officials say he survived by his wife and two young sons.