Authorities say an Ohio mother and two young girls were so badly burned that investigators can't determine if they suffered any injuries prior to a fatal house explosion and fire.

The Summit County Medical Examiner released a preliminary autopsy Wednesday saying investigators are searching for their causes of death. Records show they haven't determined exactly when they died.

A police report says Jeffrey Mather, who also died in the Jan. 11 Northfield house explosion, had previously threatened to kill himself. Investigators say Mather was found near a gas can inside the home.

Authorities say Mather showed evidence of smoke inhalation. His wife and daughters did not.

Authorities have said murder-suicide is a possibility in the explosion.

The state fire marshal's office has said investigators determined the fire was intentionally set.