Missouri ? Faulty electrical wiring may have sparked a fire that killed 10 people at a group home for the elderly and mentally ill, authorities said Wednesday.

State Fire Marshal Randy Cole said the exact cause of the blaze that gutted the Anderson Guest House may never be known because wiring was destroyed in the attic where the fire started.

But investigators found remains of improperly spliced wiring in the other end of the home. Cole said the wiring was the only thing in the attic that could have sparked the flames.

Fire damage indicated that the blaze “had burned undetected for an undetermined amount of time before breaking through into the living space of the home,” Missouri State Highway Patrol Sgt. Jason Clark said.

All 10 victims died of smoke inhalation, authorities said. Two dozen others escaped from the building, and 18 were still hospitalized Wednesday.