BYRON, Maine — The two young men and two young women drove from Massachusetts to a remote family cabin in a tiny town in Maine on Tuesday. They had come to celebrate — a sister's 22d birthday and a brother's high school graduation. Their father had plans to join them in the happy time.
But when Mark Wakelin arrived Friday, he opened the door of the cabin to find his daughter and her boyfriend lying unresponsive in a first-floor bedroom.
With no cellphone service in the area, he raced from the cabin to the nearest house for help — no answer. At the next home, he called emergency responders from a land line, only to have the tragedy compounded when the authorities reached the cabin and found his 18-year-old son and a 22-year-old woman from Attleboro lying dead in rooms upstairs.
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The four died from apparent carbon monoxide poisoning, caused by fumes from a generator running in the cabin's basement, according to Oxford County Sheriff Wayne Gallant. The cabin is off the electric grid.
The siblings were identified Saturday afternoon by the Oxford County Sheriff's Department as 18-year-old Matthew Wakelin of Mansfield and his sister Brooke Wakelin, of Attleboro, who would have turned 22 years old Saturday, Keith Norris, 23, of Attleboro, and Deanna Powers, 22, of Mansfield.
"It's very tragic; just a terrible, terrible tragedy to happen to four young people," Gallant said Saturday.
Authorities believe the victims had been dead for several days in the cabin before the father, who Gallant said lives in Braintree, arrived for the celebration.

Gallant said the generator had apparently run until it was out of gas.
The group had arrived late Tuesday evening, he said, and it appears that they turned on the generator for power to cook dinner before going to sleep, two downstairs and two upstairs.
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It is likely that "in their excitement at being in the camp, it never occurred to them to bring it outside to use," Gallant said.
Judy Boucher, who co-owns and operates the nearby Coos Canyon Cabins and Campground, said Saturday morning that the Wakelin place on Bateman Lane, a winding dirt road sparsely populated with cabins, is next to the east branch of Swift River.
She said that panicked and seeking help, the father knocked on the door of Melissa Ramey, Boucher's niece who lives in a nearby house, at about 8:30 p.m. Friday.
He "was in a bad way" when he came to the home, said Melissa's husband, James Ramey.
"He was very distraught," James Ramey said. "It's such a sad state of affairs."
The father said he had discovered the bodies of his daughter and Norris in the downstairs bedroom, Gallant said.
When the authorities responded, they found that his son and Powers had died upstairs. The family dog, a beagle, also died, Gallant said.

"It's a very difficult situation, that's for sure," said Roger Boucher, Judy's husband. "To find his daughter and her boyfriend, and later learn that his son was upstairs. . ."
Roger Boucher said he has known the father for about a year and a half, and that the father has owned the camp for about three years, using it as a summer home.
Byron has a population of just 145, according to the 2010 census, and is near Rumford.
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The original Byron township was founded in 1833 and named after the English poet Lord Byron. It features multiple picturesque camping areas near Coos Canyon, a high gorge that the Swift River flows through.
Jeff Wade has a cabin on Bateman Lane near the Wakelins.
He describes the community as close-knit and kind, and that people come to Byron to "get away from people" and focus on enjoying the scenery.
Within the community, where there are no electricity hookups or cellphone service, people are used to handling generators, Wade said.
"I couldn't believe it . . . I drove by there five times this week," he said Saturday afternoon. "I wondered why the car wasn't moving."
According to the Consumer Product Safety Commission's 2015 report, an estimated 160 people died of unintentional carbon monoxide poisoning caused by consumer products in the United States in 2011.
Generators were involved in 63 of those deaths, and for the past decade, "portable generators have been associated with more nonfire CO fatalities than any other consumer product under CPSC jurisdiction," the report said.
The Northern New England Poison Center, which covers Maine, Vermont, and New Hampshire, advises residents to keep generators at least 15 feet outside homes, with the exhaust vent facing away from the house.
The four bodies were transported to funeral homes in Rumford, then sent to Augusta to be seen by the medical examiner.
Autopsies will be performed, Gallant said.
Late Saturday afternoon, the wooden cabin stood silent in the sunshine, a sign above the front door read "Wakelins." A red plastic cup sat on a table on the front porch, with chairs alongside.
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Wade, who lives near the Wakelins, said he was shocked to learn what happened.
He has children around the same ages as the victims.
"We got calls from people who saw it on the news asking if it was us," he said.
He said he operates his generator in his garage, in a well-ventilated area.
"You just never know what can happen," he said.
Laura Crimaldi of Globe staff contributed to this report. Jennifer Smith can be reached at jennifer.smith@globe.com. Sara DiNatale can be reached at sara.dinatale@globe.com.