Pennsylvania state police believe a man fatally ambushed a state trooper responding to a domestic dispute, and also killed his wife before turning the gun on himself, investigators said Wednesday.

Lt. Col. Lenny Bandy said a man police couldn't see yelled from a window as two troopers responded to a dispute at the home of Michael J. Smith, 44, shortly after 11:30 a.m. Wednesday.

When the troopers yelled back for the man to present himself, a man they believe is Smith instead fired one shot, striking Trooper Paul G. Richey as he attempted to enter a side door, according to Bandy.

"Trooper Richey did not have a chance to defend himself," Bandy said at a news conference Wednesday night. "He was ambushed."

A second trooper radioed for backup and other troopers responded and fired multiple shots at the house to provide cover for crews to remove Richey's body from the scene. The trooper was pronounced dead at a nearby hospital.

The shooting prompted a precautionary manhunt because, although troopers believed Smith and his wife remained in the residence, they could not be sure of that at the time, Bandy said.

By 6:15 p.m., authorities were satisfied that it was likely that the suspect was in the home and they entered to find Smith and his wife, 53-year-old Nancy Smith, both dead of gunshot wounds, police said. Although ballistic and autopsy results are still pending, Bandy said it's most likely that Smith killed the trooper and his wife before killing himself.

Police don't know if Smith killed his wife before or after he killed the trooper, Bandy said.

Bandy said that although troopers fired at the house, there is no indication that any of those bullets hit the Smiths.

Richey, 40, of Franklin, is survived by a wife and two young children.

"Trooper Richey sacrificed his life rather than swerve from the path of duty," state Police Commissioner Frank E. Pawlowski said in a statement. "We will not forget his service or his sacrifice."

Paul Solle, 83, who lives about three-quarters of a mile from Smith's home, said hundreds of officers were in the area. He said he was heeding their advice to stay inside, where he was watching coverage of the shooting on TV.

Solle said he knew who Smith was but didn't know him well.

"He just seemed like an average guy to me," Solle said. "The neighbors don't associate here, not that they don't get along, it's just that they do their own thing."

Earlier in the day, a high school and elementary school were on lockdown, though children were being taken home two busses at a time or allowed to leave if their parents picked them up.

Clarion University's Venango campus also was put on lockdown. On its Web site, the university cautioned students to avoid the area or "secure yourself in a safe place and wait for police."

Gov. Ed Rendell called the shooting a tragedy and ordered flags on state buildings be flown at half-staff in honor of Richey.

Richey is the 93rd member of the state police to be killed in the line of duty. His death comes about seven months after the agency's last fatal shooting. Trooper Joshua D. Miller was killed in June during the rescue of a kidnapped child in Monroe County.