Sheriff’s Office investigators called in a heating and cooling provider to investigate the gas heating system in the cabin.
"The contractor found a significant failure in the heating system which would be consistent with carbon monoxide overcoming the residence," investigators said in a statement. "The heating unit was the only gas appliance in the home. This provides additional evidence regarding a possible carbon monoxide-related event."
The Coconino County Medical Examiner’s Office was still working to confirm the manner and cause of death, investigators said.
Jon Paxton, a spokesman with the Sheriff's Office, told KPNX-TV in Phoenix that the family drove up to the cabin late Friday evening. Investigators believe the gas leak killed them early the following morning.
Friends of the couple told the news station that the family had stayed at the cabin several times before. One friend, Rhonda Alsobrook, said that she and Megan Capitano texted back and forth multiple times just hours before the family likely died.
"I sent her this snap, 'I love you more,'" Rhonda Alsobrook said. "I won this conversation because I said, 'I love you more,' and I was the last one to say, 'I love you more.'"
Alsobrook, a professional photographer, told the news station that she was up late Friday night and into Saturday morning, finishing up the Capitano family’s Christmas photos, which were taken about two weeks before their deaths.
She said she didn’t hear from Megan Capitano again. Days later, she received the devastating news.
"I got a phone call from her sister," Alsobrook said. "She called me and told me, and it didn't really set in."
Alsobrook said she believes the family went to sleep, unaware of the danger they were in, and never woke up.
Carbon monoxide is a particularly potent danger in the winter, when cold temperatures have people turning on their heat to stay warm. Though the gas is odorless, it is sometimes possible to smell a leak from a propane gas furnace, Ponderosa Fire Chief Lee Antonides told KPNX.
“It depends on how strong the smell is, how rich, and when the furnace was last serviced,” the fire chief said. “Sometimes you can smell it, and sometimes you can’t.”
Antonides said anyone with gas heat should have a certified heating contractor inspect their home’s system before using it each winter. He said a yearly inspection is also important in rental properties.
"It's important, if you're renting a place you're not familiar with, to ask when the last time the furnace was inspected," Antonides told the news station. "Ask if there's a carbon monoxide detector in the house and, if there is, make sure it functions."
The Centers for Disease Control and Prevention reports that more than 400 people die of accidental carbon monoxide poisoning each year. Another 20,000 people visit the emergency room, and more than 4,000 of those people are hospitalized.
Symptoms of carbon dioxide poisoning, which are often described as "flu-like," include headaches, dizziness, weakness, vomiting, chest pain and confusion. The CDC said on the agency's website that people who are asleep or have been drinking can die from poisoning before any symptoms appear.
Homeowners who have gas heating systems or other gas appliances should install battery-operated carbon monoxide detectors, or electric detectors with battery backup, the CDC said. Detectors should be placed where residents can hear them if they go off at night, and the batteries should be replaced at least twice a year.
Carbon monoxide detectors should be replaced every five years.
Gas heating systems, along with gas, coal or oil burning appliances, should be serviced annually, the CDC said. Chimneys, which can become blocked by debris, should also be serviced each year.
Portable gas heaters and other gas-burning items like generators, should never be used indoors. Generators also should not be used within 20 feet of windows, doors or vents.
Friends of the Capitanos expressed shock and grief on social media.
“This is so hard to process,” Dan Matock wrote on Facebook. “My friend and his family will be sorely missed. I love you, Tony Capitano, Megan Capitano, Lincoln and Kingsli.”
Christle McGinnis described the family as “beautiful, caring souls.”
A man named Marty Gallo wrote that he was devastated by the deaths.
“My heart breaks that I wished I spent more time with you and your family,” Gallo wrote. “Tony Capitano and Megan Capitano were above and beyond the greatest souls to be around. Unwavering good in them, and it showed in their two beautiful young humans, Lincoln and Kingsli.”
Another friend, Anthony Martinez, described Tony Capitano as an incredible person.
“Hug your loved ones,” Martinez wrote. “You never know when it’s your time. RIP.”