Heckler said Tuesday night that a Pennsylvania State Police investigation indicates that Gary Reitnauer went to the garage of an adjacent home on the family's property and started the car following a disagreement with his wife, Michelle.
State Police were called to the home in Milford Township in rural Bucks County at 11:20 p.m. Monday. They found the structure filled with high levels of carbon monoxide from the running vehicle, Lieutenant Vincent D'Angelo said in a news release.
Investigators "believe the husband committed suicide and each ... of the family members succumbed to carbon monoxide when they went to check on him and tried to rescue him," Heckler said.
The cause and manner of death must still be confirmed by the county coroner's office, he said.
State Police have found no note, but the garage door handle had been knocked off, "which suggested that the husband went in there and did not intend to be disturbed or rescued," Heckler said.
He said the circumstances also indicate that his wife went to the garage and broke the window of another door in an apparent attempt to rescue him, but was apparently overcome by the deadly fumes and was found inside.
The 16-year-old daughter, Kimberly, then apparently went to the kitchen adjacent to the garage and was found on the floor there, Heckler said. Ten-year-old daughter Jamie is believed to have done the same and was barely alive when rescuers arrived. She later died.
The fire department responded and discovered the victims, but emergency workers were unable to revive them. All four "appeared to have died from carbon monoxide poisoning," D'Angelo said.
Stunned friends and neighbors recalled the family Tuesday as happy and outgoing. Property records show the couple bought their ranch-style home at the end of a long driveway in 1996.
"Good man," a nephew, Rob Zern, told reporters as he left the home. "The family was trying to save each other and it didn't work out ... don't know what all went wrong, but it's a tragedy all around."
The Quakertown Community School District announced the deaths on its website and said counselors would be made available to help grieving students and teachers.
"She was just the sweetest soul, the one taking care of everyone else," Quakertown math teacher MaryAnn Byatt said on the district's website. The site said Kimberly, a junior, was a gifted student, receiving the highest possible score on the advanced placement calculus exam at the end of her sophomore year. She also sang in the chorus and played in the jazz band, and was set to compete at a band festival in Erie.
Her sister was a fifth grader and took part in her school's Reading Olympics Team. Like her sister, she played in the school band and sang in the chorus. She wanted to become a veterinarian, the site said.
Six high school classmates of Kimberly Reitnauer placed flowers on the family's mailbox Tuesday afternoon, then formed a circle, clasped hands and prayed. Afterward, they remembered their friend as a highly intelligent student near the top of her class, and as a talented musician who played piano and trumpet. She was happy, kind and humble, they said.
"Everyone here loved her. She always had a smile on her face. Her whole family did. They were just the happiest people, and they made everyone else feel the same way," said Aislinn Strohecker, 17, a close friend and neighbor.
Neighbors said there was no inkling of trouble in the Reitnauer home.
Michele Reitnauer, 58, gave Christmas cookies every year to a well drilling company down the gravel road, and would fetch the company's mail when she got her own, according to Gloria Mayberry, a secretary at the firm. Gary Reitnauer, 59, known as "Ozzy," would use the bucket on his John Deere tractor to take his trash can to the end of the drive, a cigar usually hanging from his mouth, she recalled.
The children were adopted from China, according to Maggie Chambers, a neighbor and Strohecker's mother. She said they were "just the sweetest family."
"It's not that kind of family. For me to even think for a minute that this was a deliberate thing, it's just not them," Chambers said. "It's not."