Four family members were found dead on New Year's Day inside a cabin outside of Flagstaff. Firefighters believe carbon monoxide poisoning may be to blame.

The victims have been identified as 32-year-old Anthony Capitano, 32-year-old Megan Capitano, 4-year-old Lincoln Capitano, and 3-year-old Kingsli Capitano of El Mirage.

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The family was spending the end of 2017 at a friend's cabin in Parks.

Another family friend called the Coconino County Sheriff's Office on Monday afternoon because they hadn't heard from the family in a few days.

The tragic discovery was made during a welfare check.

When the first responders arrived at the cabin, they say there was a strong odor of burned propane gas coming from the cabin.

Firefighters were called out and when they went inside the cabin, they found the bodies of the four family members.

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The Coconino County Sheriff's Office said on Tuesday afternoon that a contractor brought out to inspect the home found a "significant failure" in the heating system at the cabin that likely led to the carbon monoxide poisoning.

The heating unit was the only gas appliance in the home, and investigators said Wednesday that there were no carbon monoxide detectors in the home.

"There is nothing to think about. It's just tragic. It's just a big hole in all of our hearts, that only Tony and Megan and their children can fill," said Dan Matock, a family friend.

Matock had known the father, Tony, for years.

"Tony just had a magnetic smile and spirit about him and Megan was a compliment to that," said Matock. "Just the perfect couple. I mean, I try to emulate my relationship with my girlfriend and my children after Tony and Megan."

The company Discount Tire released a statement Wednesday about their employee, Tony:

"Discount Tire is deeply saddened by the loss of one of our own Discount Tire employees in Arizona. Tony was an upstanding member of our team and our thoughts and prayers are with his family and friends. Out of respect for the family, at this time we are not able to provide any further information."

The Medical Examiner's Office will conduct an investigation, CCSO said.

Carbon monoxide is a colorless, odorless gas that can be deadly, often referred to as a "silent killer."

The Centers for Disease Control and Prevention recommends people equip their homes with carbon monoxide detectors to protect themselves.

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