Oak Grove, MO – Oak Grove police said they are investigating a possible carbon monoxide poisoning death on Monday night.

A teen died and two other people are in critical condition after they were found in a fourplex with a running car inside the garage of the unit.

A resident of a fourplex called 911 at about 6:30 p.m. Monday when he got home from work and noticed a strong odor, police said. Emergency crews said they found unusually high levels of carbon monoxide in the man’s unit. A check of the adjoining unit showed twice the level, so emergency workers forced entry into the unit.

Emergency workers said that is when they found a woman in her 60s and two teenagers unconscious. The teen who died was the woman’s granddaughter and the other teen was a friend of the victim, police said.

Police have not released the names of any of the victims. They were all last seen on Sunday night.