Authorities have found evidence that accelerants were used to start a fire at a Massachusetts home in which a family of five was found dead in an apparent murder-suicide.

Berkshire District Attorney Andrea Harrington on Monday said investigators located evidence of an accelerant in different parts of the Sheffield home, including two 20-pound (9-kilogram) propane tanks on the upper floor.

Harrington says there is "overwhelming evidence" that 41-year-old Luke Karpinski killed his wife, 41-year-old Justine Wilbur, their 7-year-old twins, Alex and Zoe, and 3-year-old son, Marek, last Wednesday morning before starting the fire and killing himself.

Authorities have not said how the family died and autopsy results are pending, but Harrington says police did not find any evidence of guns in the home.

The investigation is ongoing.