The carbon monoxide poisoning of a Denver family of four happened overnight, Pitkin County sheriff’s spokeswoman Marie Munday said Monday.

Since the Lofgrens — Parker and Caroline and their children Owen and Sophie — were found in their beds Friday afternoon, it was assumed that they just went to sleep and never woke up.

The culprit turned out to be a broken pipe in a crawl space under the multimillion-dollar home on Popcorn Lane, which is about four miles east of Aspen.

The pipe or a joint on the pipe had somehow disconnected, said Munday. It was part of the heating and snowmelt system for the five-year-old house.

“It was when the snowmelt system kicked in that this happened,” said Munday.

An investigation led by the sheriff’s office is ongoing to try to determine whether any entity is at fault, although at this point is seems like “just a freak accident,” said Munday. “The system has been there for more than four years, so it’d be hard to find some kind of negligence.”

It’s unclear to investigators whether the Lofgrens arrived on Wednesday or Thursday to the home, but its owner stayed in the home the weekend before without incident.

“The lesson is get a carbon monoxide detector in your home,” she added.

Aspen resident Elizabeth Milias, who was good friends with the Lofgren family, is starting an awareness program — the Lofgren Initiative — to get more carbon monoxide detectors in homes. Thanks to her lobbying efforts, Ace Hardware is offering 10 percent off the devices, along with free delivery.

The city of Aspen is also considering amending its building codes to make carbon monoxide detectors a required feature in new and remodeled buildings. Pitkin County’s building department is also encouraged to join in the effort.

Carbon monoxide is an odorless, colorless gas that is produced by faulty appliance systems. It produces flu-like symptoms and can be fatal quickly; carbon monoxide poisoning claims about 500 lives per year and sends another 15,200 people to emergency rooms. Exposure to the gas occurs more frequently in the fall and winter when people are more likely to use some kind of heating system in their homes, and its danger has heightened with modern, airtight homes. Ventilating by opening doors or windows can help to alleviate any suspected carbon monoxide leak, but professional help is highly recommended if anyone is feeling ill.