Authorities have been baffled by the deaths since last September

By Tara Fowler
Updated January 27, 2015 06:30 PM
Grant Hindsley/Grant Hindsley/AP

Relatives of a family of five who died mysteriously in Utah last September are finally getting some closure in their deaths – though it may not be the answer they hoped for.

Police said Benjamin, 37, and Kristi Strack, 36, murdered their two youngest children and possibly killed a third with a combination of drugs including methadone, according to

The bodies were discovered on Sept. 27 by an older son, Janson McGee.

The parents were found with cups of red liquid next to their bodies, while the children were discovered lying on and around the bed, covered with blankets up to their necks, with empty bottles of liquid methadone and boxes of cold and flu medication nearby.

An autopsy determined Tuesday that all five died due to “drug toxicity,” reports. Police initially suspected that poison was the likely culprit.

The third child’s death, 14-year-old Benson, was “undetermined,” according to authorities.

“There are some questions we can’t answer and may never be able to answer,” said Springville Police Chief J. Scott Finlayson.

Relatives told PEOPLE in October that they suspected the Stracks had killed their children and committed suicide themselves.

“They had isolated themselves from neighbors and some of the family,” Benjamin’s brother Isaac Strack said, “and it had been awhile since Ben had been to work.”

He added: “Some of the changed behaviors before their deaths seemed out of place and didn’t make sense at the time. But looking back now, they make sense. And now we want to speak out to prevent other people from having to endure what we are enduring.”

Police said that they found no evidence to suggest that the children had been forced to take the drugs, nor any evidence that they took them willingly.