The deadly blaze that broke out at an assisted living facility in Massachusetts earlier this month was sparked accidentally by either a malfunctioning oxygen machine or, possibly, a resident smoking,

An investigation into the source of the fatal fire at a Massachusetts assisted living facility last week classified the cause as "undetermined," though officials believe it was an accidental ignition

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,