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,

The fire began in a resident’s room in an assisted living facility in Fall River, where investigators found an oxygen machine and “smoking materials.”

The July 13 fire killed 10 people and injured at least 30. Its exact cause might never be determined, officials said.