FALL RIVER, Mass. (AP) — 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, officials said Tuesday.

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

Officials announced a preliminary investigation shows a oxygen tank malfunction or smoking may have caused the deadly Fall River assisted living facility fire that claimed the lives of 10 last