Washington: Facebook slaying suspect Steve Stephens was undone by a 20-piece Chicken McNuggets and an order of fries.

The man who shot a Cleveland retiree at random and posted video of the killing on Facebook pulled up to the drive-through window of a McDonald's restaurant outside Erie, Pennsylvania, and waited for his order.

It was late on Tuesday morning, almost lunchtime, and authorities were in the third day of an intensive manhunt for Stephens.

Now, more than 160km from the shooting, his time on the run was nearly up.

The attendant who took his money recognised him as the suspect and dialled 911. Stephens pulled up to the next window, where restaurant owner Thomas DuCharme jnr and a supervisor tried stalling him by telling him his fries were delayed.

Stephens didn't want to wait. He took his McNuggets and whipped out of the parking lot, nearly hitting Gail Wheeler, 54, a retail operations manager from Erie who was on her way home from the grocery store.

"Two seconds later, I hear these sirens, and they come whipping past me," she told The Associated Press.

Wheeler followed behind for a couple of kilometres. She said the chase slowed suddenly when the road narrowed from four lanes to two.

One of the pursuing troopers picked his spot - in front of an abandoned school - and hit Stephens' bumper to get him to stop. The Ford Fusion did a half-turn and came to rest at the curb.

Police were starting to get out of their cruisers when "I heard a shot. It was loud and distinctive," Wheeler said.

"The next thing I know, they're approaching the car. The one officer just shook his head. He was closest to the car ... They had their guns out but when he shook his head, they lowered their guns."

Authorities said Stephens fatally shot himself.

Lifeline: 13 11 14

Suicide Call Back Service: 1300 659 467.

MensLine Australia: 1300 78 99 78.

AP