Investigators looking into an accident in Connecticut that critically injured a Littleton tractor-trailer driver are no closer to identifying suspects in the crime.

Wayne Tapley, 48, was northbound on Interstate 95 in his truck at about 8:30 p.m. last Thursday when he was struck by a rock that came through his windshield, police said. The rock was thrown by an unknown person or persons.

Tapley was listed in good condition Thursday at Yale New Haven Hospital in New Haven, Conn., according to Mark D’Antonio, hospital spokesman.

The truck driver will be transferred today to Eastern Maine Medical Center in Bangor for further treatment.

“We are thoroughly investigating the incident, but we still do not have any suspects at this point,” Sgt. J. Paul Vance, Connecticut Department of Public Safety spokesman, said Thursday. “We are still urging people who may have information about the case to call us.”

Investigators think Tapley may have been dazed or knocked unconscious by the rock, causing him to lose control of the vehicle and sideswipe a bus.

The tractor-trailer then careened off the median barrier, swerved back across the highway and plunged down a steep embankment.