Alabama State Trooper investigators were trying to solve a mystery Wednesday.

A 15-inch wheel that apparently rolled uncontrollably down Interstate 65 north of Athens early Wednesday, bounced onto the hood of an 18-wheeler, smashed through the windshield and killed the driver.

“We don’t know where it came from or from whom, but it struck the windshield with such force that the driver of the truck was killed instantly,” said Limestone County Coroner Mike West. The coroner said the driver died from massive head injuries.

West pronounced Barry Keith Smitherman, 47, of Summitt Ridge Road, Madison, dead at the scene. Smitherman had just left the Huntsville area and was traveling north on the interstate just north of Athens when the accident occurred just after midnight, according to state troopers who are investigating the wreck.

Troopers Wednesday were attempting to locate the source of the runaway wheel.

“We’re still working on it and no have leads as yet,” a trooper spokesperson in the Decatur office said.

West and troopers are speculating that the wheel spun off some type of multi-wheeled vehicle or a lo-boy trailer without the driver knowing it. West said it is unlikely the wheel fell off the back of a trailer or truck because of its speed and path before striking the 18-wheeler.

“It appeared it hit the truck head-on and jumped into the windshield. It entered the cab of the truck and exited through the back top. The wheel was found about a quarter-mile south or behind the 18-wheeler,” West said.

Smitherman was employed by First Fleet in Huntsville and had left Bardcor in Huntsville with a load of materials, West said. He did not know what the trucker was carrying in his trailer or where he was headed at the time of the 12:10 a.m. accident.

“It occurred at the 354-mile marker, just outside the Athens city limits,” West said. “After the driver got hit in the head, the truck left the pavement and apparently got stalled in the mud on the east side of the interstate. It came off the road and to a stop.”

Authorities said it is highly unlikely the wheel came off a vehicle on the other side of the interstate because it would have had to cross the median and go straight down the northbound lane. West said it is likely the wheel came off a vehicle or trailer in front of the 18-wheeler.