PUTNAM, Conn. (AP) _ Investigators say the cause of a house fire that killed two girls in Putnam last week may never be known because the damage was so extensive.

The fire in the early morning hours of Jan. 22 killed 6-month-old Ava Auger and her 3-year-old sister, Alexis, and destroyed the multifamily home on Prospect Street.

Fire marshals and police believe the fire was an accident. But they said Tuesday that the cause probably will remain undetermined.

The girls’ mother, Lauren Auger, and Ava’s father, Michael Bandlow, escaped from the burning home. Laren Auger is pregnant and due in a few weeks.

Bandlow was among dozens of people who gathered in Putnam Tuesday night for a candlelight vigil in memory of the two girls.