CENTER TWP — The driver of a pickup truck that crashed Tuesday morning was killed by blunt force trauma, an autopsy revealed.

Investigators did not immediately know what caused the wreck on Unionville Road that left 63-year-old Steven M. Zulick dead, and wondered if a medical emergency could have been to blame.

But the findings of the autopsy conducted later Tuesday seemingly forced the state police investigation back to square one as authorities search for the reason why the Butler area man crashed.

Speed, alcohol and drugs are not believed to be contributing factors, investigators said. And Zulick’s cell phone was turned off and in his jacket pocket when emergency crews found the wreckage.

Police said Zulick was driving a 2003 Chevrolet Silverado east on Unionville Road about 7:55 a.m. when the pickup left the south side of the road and struck a tree in a home’s front yard.

He was not wearing a seat belt. But authorities could not say for certain if he would have survived the crash had he been belted.

“He hit the tree pretty hard,” said Butler County Chief Deputy Coroner John Hanovick, who pronounced Zulick dead at 8:10 a.m.

Investigators said at least one motorist was traveling near the truck and did not report seeing Zulick driving erratically before the wreck.

The truck left no apparent skid marks before it went off the road.

“We don’t know why he just went off the road,” Hanovick said. “That’s why we did the autopsy, to see if he may have had a medical issued before (the crash).”

The autopsy determined Zulick died of internal chest injuries. Results of routine toxicology tests are pending, authorities noted.