Fourteen months after a deadly five-alarm fire ripped through a West Chester senior citizen residence, federal investigators have concluded their investigationwithout determining a cause.

The U.S. Bureau of Alcohol, Tobacco, Firearms, and Explosives on Thursday released the findings of its investigation into the fire at the Barclay Friends senior living complex that killed four residents and displaced more than 100.

Many questions remain unanswered. ATF said it could not determine the fire’s point of origin or why the building’s sprinkler valve was turned off during the blaze.

The fire broke out in the personal-care section shortly before 11 p.m. on Nov. 16, 2017.

ATF officials reiterated Thursday that the fire started in the rear back patio. In December 2017, ATF spokesperson Charlene Hennessy said investigators were working to find out whether a cigarette, an electrical fault, or something else on the patio sparked the blaze. Ultimately, federal investigators, working alongside Chester County authorities, couldn’t make that determination.

They did, however, determine that smoke and fire alarms worked properly, causing the fire doors to shut and activating sirens and strobes, which prompted employees and residents to evacuate quickly, officials said.

But fierce winds, which battered the building’s flammable vinyl siding, fueled the fire, investigators said. The flames spread to the roof and other parts of the building, becoming a five-alarm fire in only a half-hour.

When they arrived at the charred scene at 700 N. Franklin St., investigators found the building’s main sprinkler valve in the off position. They eventually determined the valve had been in that position during the fire, ATF said, but officials did not know when it had been turned to that position or by whom.

The fire claimed the lives of four residents: Mildred E. Gadde, 93; Theresa Malloy, 85; and a married couple, Delores G. Parker, 89, and Thomas F. Parker, 92

Lawyers for the families of three of the victims told the Inquirer in April that an engineer for the home had informed them that no water had been flowing to the sprinkler system that night.

Attorneys with the Robert Mongeluzzi and McEldrew Young law firms, which represent the Malloy and Parker families, said Thursday that their clients' lawsuits against Barclay Friends were settled confidentially a few months ago. They said they believe the ATF’s findings bolster their ongoing suits against other companies affiliated with the complex’s fire-suppression system.

Robert Mongeluzzi and Dan Purtell of McEldrew Young both said that they believe a lit cigarette caused the fire, and that their investigations will prove that.

Independent experts have told the Inquirer that they believe the home’s fire-suppression system was flawed in its design. On recordings from that night, firefighters — some of whom ran in without breathing apparatuses — can be heard complaining about lack of water pressure, with one saying: “There is no water pressure at all at the scene."

ATF has maintained that the fire was not set.