A couple and three of their children were found by an older son in the parents' bedroom in Springville, Utah, near Provo, police Lt. Dave Caron said.
A preliminary autopsy found they weren't killed by violent assault. A test of air in the house by firefighters did not find any carbon monoxide, but investigators said the family could still have been poisoned by gas if it dissipated before the test.
There were no signs of a struggle, and police didn't find any notes or other evidence that would indicate what killed them, Caron said.
"I really don't like an unsolved mystery ... those kind of things grate on you," he said.
'We Haven't Ruled Out Anything'Medical examiners were analyzing blood samples from all five people, but the process usually takes at least six weeks and sometimes months. Police also intend to analyze beverages and food the family might have consumed.
Asked if foul play has been ruled out, Caron said, "I don't rule out anything ... We haven't ruled out anything except there was no violent trauma. We're going to look at everything."
The bodies were found Saturday night about 45 miles south of Salt Lake City. They were identified as Benjamin Strack, 37, his wife, Kristi, 36, and three of their children, Benson, 14, Emery, 12, and Zion, 11.
The family was gathered in the room with a big-screen TV, Caron said.
An older son, about 18, made the discovery after going to the duplex when he did not hear from the family as expected. His name was not released.
Jim Phillips, a friend acting as a spokesman, said the Strack family wasn't ready to comment.
"The family is obviously grieving their loss," he said. "They're coming together and have asked for understanding and patience."
Money Problems?Benjamin Strack worked off-and-on for six to seven years at AK Masonry, a bricklaying company, and had borrowed money in the past, owner Alex Short said.
"He borrowed some money to pay rent," Short said. "That money still hasn't been repaid."
Short said Strack was a good employee when on the job but often didn't show up for days at a stretch.
"We hadn't seen him for the last two weeks," Short said.
Court records show Benjamin and Kristi Strack pleaded guilty to misdemeanor forgery charges in 2008 and disorderly conduct the following year.
Police said the family's financial history and other personal details aren't part of their investigation, but the scope could widen if they find foul play was involved. Phillips declined to comment.
The duplex is located on a road to a high school in Springville, a city of 30,000 people south of Provo.
The children were homeschooled, neighbors told the Deseret News. The family was kind, but kept to themselves and the children were shy, Reilly Strecker, who lives in the other half of the duplex, told the newspaper.