Officials are investigating whether Wednesday’s row house fire that killed 12 people, including eight children, in Philadelphia began when a child playing with a lighter accidentally set a Christmas tree alight. A search warrant application filed Wednesday referenced “information that a child age 5 or under” had been playing with a lighter near the tree. The child cited in the application lived in the home, where at least 25 other people were spread across two overcrowded units. Two sources familiar with the investigation told The Philadelphia Inquirer that the child told first responders that the tree was ablaze. The child has since been interviewed by investigators, though no charges are expected under Pennsylvania law. A federal agent with the ATF said Thursday that nothing has been ruled out yet, and that those scrutinizing the tragedy are using “all the technology that we can bring to bear.”