MERCER — Three weeks after a tractor-trailer struck and killed a retired state police officer standing on a highway near the Butler-Mercer County line, investigators still don't know the identity of the truck driver.

"We had a couple of leads," Trooper Dan Sindlinger said Tuesday, "but they didn't pan out."

Billy Ray Williams Sr., 64, of Erie had been driving east on Interstate 80 in Wolf Creek Township on the evening of Feb. 18 when his Ford Crown Victoria malfunctioned.

It was about 6:15 p.m. when he apparently stopped his car on the highway and got out.

A witness, who was driving in the right lane behind the tractor-trailer, told investigators Williams walked across the front of his car toward the driver's side and stepped into the left lane.

Police believe the truck driver was changing lanes and trying to avoid Williams' car.

"We don't know if the driver knew he hit someone or not," Sindlinger said. The truck continued eastbound.

Investigators suspect Williams was hit by the cab of the truck, which was hauling a box trailer or a flatbed with sides.

Williams, who retired in 2006 after a more than three-decade career with the state police, was taken to the Grove City Medical Center where he was pronounced dead about an hour later.

Mercer County Deputy Coroner John Libonati said Williams died of head and chest injuries. No autopsy was done.

Police have only received "several calls" about the crash, which remains under investigation. A police accident reconstruction report is not completed.

Sindlinger said police are preparing flyers to be posted at truck stops on I-80 between the Ohio state line and Clarion County.

"We're hoping someone sees the flyers and comes forward with information," he said.

Williams joined the state police in 1969. He served as Mercer's station commander from 1993 through Sept. 11, 2000.

He retired as staff lieutenant of Troop E headquarters in Erie on Christmas Day 2006, the day he turned 60, after more than 35 years of service.

Among his survivors are eight sons and three daughters. Four of his children live in the Grove City area.

His children have unlisted telephone numbers and the Butler Eagle could not reach them for comment.

Anyone with information about this fatal crash is asked to call police at 724-662-6162.