GROTON, MASS. >> Investigators say the cause of a fire in a Groton home that killed two people will remain undetermined, but that it does not appear suspicious.

The fire in the 19th-century home Jan. 28 killed 66-year-old Douglas Palmisano and a woman whose name has not been released pending formal identification by the medical examiner.

The state Fire Marshal announced Monday that the late-night fire started on a couch in the first-floor living room.

The residents were known to use an electric space heater in that area and to smoke while sitting on the couch, but because damage was so extensive the exact cause could not be determined.

State Fire Marshal Peter Ostroskey and Groton Fire Chief Steele McCurdy said the home apparently did not have any smoke alarms.