This is a true story that occurred in Louisiana.
The real Leonard Fagot died in 1978 and 2 of his daughters Carol Ann Fagot Applegarth Holland and Nancy Fagot both died in 2009
He was in the 22nd Marine regiment during World War II. This was part of the 6th Marine Divisionn and you can see the division insignia on his headstone at the beginning of the movie..
Based on the book by Carol Donahue and Shirley Hall titled Deadly Relations: A True Story of Murder in a Suburban Family. Donahue and Hall are the daughters of Leonard Fagot, played by Robert Ulrich here.