Police in eastern Missouri say a car left running in a garage overnight caused the deaths of three people inside two separate duplex units in Union.

The St. Louis Post-Dispatch reports that on Tuesday, officers who had been sent on a welfare check found 74-year-old Edward Huddleston and his dog dead in one unit.

Firefighters called to the duplex then found 85-year-old Verlyn Branson and his son, 58-year-old John Branson, dead in an adjoining unit.

Union Police Capt. Richard Neace said a vehicle left running in Huddleston’s garage overnight released the carbon monoxide that killed all three.

Neace says no foul play is suspected, and investigators think the car may have accidentally been left running.