BOSTON -- The investigation into a South Boston fire that claimed the lives of two young sisters continued Monday.

NewsCenter 5's Gail Huff reported that Acia "C.C." Johnson, 14, and her sister, Sophia Johnson, 2, were killed when flames tore through their townhouse at 154 W. Sixth St. at about 3 a.m. Sunday.

VIDEO: Home Searched In Fatal Fire

An accelerant-sniffing dog joined investigators at 64 West Seventh Street, where officials are searching an apartment around the corner from the fire scene. Officials identified the occupant as a friend of Anna Reisopolous, 34, the mother of the girls who died in the fire. Reisopolous was reportedly in a fight with the woman prior to the fire, Huff reported.

"There has been a history of violence in the house, a history of drug use by the mother and other friends. The people knew something was going to happen -- nothing like this, though," Rep. Brian Wallace said.

Friends said the two sisters were inseparable and when the fire broke out they ran to take cover in an attic closet on the third floor because they were too afraid to jump from the burning building. The girls died in what is being investigated as an arson fire, officials said.

Friends of the young girls said that they are furious to learn that police are looking for a possible suspect in their neighborhood.

"I don't think they are going to go to any court systems pretty quick. I know if I found out that someone did this, we'd hold judge, jury and execution right on the spot," resident Danny Zyskowski said.

"These poor two little girls did nothing wrong and were the recipients of this kind of action," Wallace said.

Officials have not disclosed how the fire started.