Authorities have not ruled out homicide as they investigate how twin brothers dependent on breathing ventilators died during a power outage in the Northern California town of Valley Springs.

Calaveras County coroner's officials believe identical 22-year-old twins Ryan and Joshua Hall may have died from asphyxiation when their back-up ventilators also failed during the power outage Tuesday night, Fox's KTLX-TV in Sacramento reported.

The brothers had muscular dystrophy and were unable to breathe without the ventilators.

“It could be medical … possible homicide. It can go in any direction. We’re just not far along at this point and time to make any good determinations,” Calaveras County Sheriff Gary Kuntz said.

Authorities continue to investigate if the power outage contributed to their deaths and why a backup system failed.

“It appears they’ve been on the life-support system since they were two years old,” Kuntz told KTLX.

The brothers' stepfather told the TV station that when the electricity went out their mother, Julia Hall, who is also their full-time caregiver, thought her sons were merely sleeping. But when she checked on them again a half-hour later she realized they weren’t breathing and called 911.

Officers who responded to the home administered CPR, but failed to revive them.

“It’s sad because a lot of people in the Valley Springs area community knew these two boys and knew the mother,” Kuntz said.

The twins' stepfather said they had recently moved from a full-time care facility in Elk Grove to their mother’s Valley Springs home. No full-time nurses were assigned to help at the home.

The brothers' deaths saddened neighbors in the small town east of Stockton.

“I heard and I just started crying,” neighbor Kayte Dollens said.

Another neighbor, Megan Dollens, told KXTX-TV of Sacramento she couldn't imagine the family's pain.

"I honestly don't know what to think about this because it's awful," she said. "I can't imagine what their parents are thinking."

Kuntz told KTLX that Hall had been "very cooperative" with investigators. Still, "we're not ruling anything out."

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