WEST CHESTER (AP) — Investigators say the fire that claimed the lives of four at a Pennsylvania senior living community began on an outside patio behind the facility.

The Philadelphia Inquirer reports a spokeswoman for the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives said Thursday while the patio was the fire’s starting point, they have yet to determine what ignited the fire.

Arson and foul play have been ruled out.

Four people, 93-year-old Mildred Gadde; 85-year-old Theresa Malloy; 89-year-old Delores Parker; and her husband, 92-year-old Thomas Parker died in the overnight fire at Barclay Friends in West Chester Nov. 17.

More than two dozen were injured and 133 residents have been displaced.

ATF spokeswoman Charlene Hennessy says the fire was “purely accidental.” She says the agency hopes to release more findings next week.