The bodies of Gary and Michele Reitnauer were found in a house in Milford in the Philadelphia suburbs late Monday with their daughters Jamie, 10, and Kim, 16.
Bucks County District Attorney David Heckler said Wednesday Reitnauer, 59, apparently decided to take his own life after a fight with his wife, WFMZ-TV in Allentown reported. He said Reitnauer parked his car in the garage of an empty house on his property and broke the garage door handle, leaving the car running.
His wife's body was in the garage and the two daughters in the kitchen next door.
Paul Moser, who knew the family, was shocked by the deaths. He described the Reitnauers as "always laughing and carrying on and always had a good word to say."
The couple adopted their two daughters from China.
"She was one of the most amazing people that I have met," Alicia Loch, who was in Kim's class at Quakertown High School, said.