Callihan said that the preliminary investigation suggests that the elder Frew and his family were victims "of a pre-planned murder" plot, and that he acted in self-defense. Police also found a can of gas and lighter fluid in the Ruckingers' car.
Ballistics and toxicology tests are pending, investigators said.
Authorities are still exploring possible motives, but say there may have been burglaries and robberies at the Frew residence in the past.
A relative, Virginia Cruse, said the daughter and mother did not get along, but that she had no idea what spawned Friday's tragedy. The daughter had "a hatred toward the family," she said.
When Josephine was about 20, she and a boyfriend trashed her parents' home and stole items including a pistol, then fled to Pittsburgh, Cruse said. After that, she said, "more or less, they disowned her."