Credit: MTV Photo: Buckwild's Shain Gandee Dead at 21

Yesterday, news broke that Buckwild fan favorite Shain Gandee passed away tragically, and since his body was found — alongside his uncle David Gandee, 48, and their friend Robert Myers, 27 — authorities have been working tirelessly to piece together the puzzle of his mysterious death.

Now we can sadly confirm that it was carbon monoxide poisoning that killed the three West Virginia residents after the truck’s tail pipe was submerged in mud, clogging the exhaust and causing the cabin to fill with gas.

The Kanawha County Sheriff's Department told CBS News that “autopsies completed Tuesday confirmed the three men died from the gas” and their deaths have been “ruled accidental.”

Earlier today, Shain’s cousin, Ashley Gandee Lewis, updated her shop’s Facebook page (Gandee’s General Store) with some new information on the case, explaining that Shain wasn’t in pain when he passed.

“I just wanted to let everyone know that the family feels that Shain died peacefully in his sleep without pain or suffering. That it probably was carbon monoxide,” she wrote. “They are making arrangement[s] now for his funeral. Nothing is confirmed but they are thinking Saturday."

And after his official cause of death was released, she wrote, “It has been confirmed that Shane died of carbon monoxide poisoning,” along with a few other updates about the fundraising to help offset the cost of funeral services.

Our thoughts go out to Shain, David, and Robert’s friends and family at this difficult time.

Sources: CBS News, Facebook