BYRON — Accidental carbon monoxide poisoning is the official cause of death of four young people from Massachusetts whose bodies were found along with a dead dog in a remote Oxford County cabin on July 17, according to the state medical examiner’s office.

“The cause of death was confirmed to be carbon monoxide toxicity for all 4 decedents, the manner was ruled accidental by Dr. (Clare) Bryce, Deputy Chief Medical Examiner,” spokesman Mark Belserene said in a Monday afternoon email.

Police assumed as much, but were awaiting the toxicology tests to confirm it. Belserene said the toxicology test results did not show any substances present other than carbon monoxide.

Brooke Wakelin, 21, of Attleboro, Mass., her brother Matthew, 18, of Mansfield, Mass., Keith Norris, 23, of Attleboro, Mass., and Deanna Powers, 22, of Mansfield, Mass., were found dead in the Wakelin family cabin by deputies responding to a 911 call placed at 8:34 p.m. July 17, after the father of the Wakelin siblings arrived at the cabin.

The family had planned to celebrate Brooke Wakelin’s 22nd birthday on July 19, Sheriff Wayne Gallant said at the time.

The young adults and a beagle were staying in the cabin without electricity and an empty generator was found in the basement. Investigators believe the group, who arrived at the cabin on Tuesday, July 14, started the generator to plug in the refrigerator, Gallant said.

“Sometime that night … they went to bed and the generator remained running,” the sheriff said. “The generator ran through its entire tank of gas.”

The fumes from the generator, which should have been moved outside while running, filled the cabin and overtook the group and the family pet, he said.