MINNEAPOLIS (WCCO) — Two grandparents and their 4-year-old grandson were found dead in their Wisconsin home Sunday morning, according to the Sawyer County Sheriff’s office.

Deputies reportedly arrived at the home in the town of Radisson at around 11:20 a.m. There, they found the bodies of 61-year-old Seven Michael Ryan and 60-year-old Carolyn Marie Rindahl along with their grandson. Investigators noted signs of carbon monoxide poisoning in the victims, though a toxicology report from the coroner is still pending.

Responding deputies also noticed a furnace in the home that was improperly installed, and detected carbon monoxide inside the house.