putting out the fire without the supply being shut down. >> reporter: planes dropped retardant and by dawn, the fire was mostly contained. in addion to those killed, more than 50 others were injured, some critically. and now the questi, what happened? the local gas company pacific gas and electric says 30-inch gas line, one that's 40 to 50 years old likely ruptured. >> we are constantly working every day to make sure we're maintaining the integrity of that system. >> reporter: as the investigation intensifies, people stunned in this community rocked by the disaster hope for answers. now, as for those residents from those neighborhoods, there's no word yet on when they'll be allowed return and see what's left of their homes. alex? >> leanne, there have been some who have wondered why the national transportation safety board is leading this investigation. is it because of their vast experience with these major catastrophes like this? with plane crashes and alike? >> reporter: and because they are in charge of gas lines.