The cause of a fire at a Massachusetts assisted-living facility that left 10 people dead remains undetermined for now as officials investigate whether smoking materials and an issue with a medical oxygen machine may have been factors,

Nine people were killed and one was critically injured in a fire at an assisted living facility in Fall River, Massachusetts, authorities said. Fall River Fire Chief Jeffrey Bacon called the fire at Gabriel House "an unfathomable tragedy.

Investigators may never know for certain what sparked the fire on the left side of the U-shaped assisted living facility.