GENEVA, Alabama (CNN) -- Authorities in a southern Alabama community are trying to determine what caused a man to open fire on family members and apparent strangers on Tuesday, killing 10 people, before turning the gun on himself.

By the time McLendon ended his rampage, he had fatally shot his mother and set fire to her house, and killed his grandparents, his aunt and uncle, the wife and child of a sheriff's deputy, and three other people, according to King and the coroners of the two counties where the shootings occurred.

The mother had been shot, he said.

The gunman then went east into Geneva County. There, he shot his grandfather, grandmother, uncle and aunt as they sat on a porch in the nearby town of Samson, said Geneva Coroner Max Motley.

The wife of a sheriff's deputy who lived in a house across the street was also killed, along with her toddler, Motley said. Both were shot. Watch deputy ask for prayers for wounded daughter »