A fire investigator said on Tuesday that a gasoline-fueled arson blaze spread "in a very rapid, quick and violent manner" through a Cheshire house where Jennifer Hawke-Petit and her daughters, 17-year-old Hayley and 11-year-old Michaela died in a 2007 home invasion.
Paul Makuc, a state fire marshal, testified on Tuesday during the trial of Steven Hayes, one of two men charged in the killings.
Prosecutors have said Hawke-Petit was strangled and her daughters died of smoke inhalation.
Makuc said the fire began in a family room where the mother's body was found, and quickly spread to the second floor into the girls' bedrooms.
Prosecutors say Hayes and Joshua Komisarjevsky, who awaits trial, tied the girls to their beds and poured gasoline on or around them before burning the house.