PHILADELPHIA (AP) — Investigators are looking into whether a 5-year-old who was playing with a lighter set a Christmas tree on fire, sparking a conflagration that killed 12 family members in a Philadelphia rowhome, officials revealed Thursday. That disclosure was included in a search warrant application as city and federal investigators sought to determine the cause of the blaze, the city’s deadliest in more than a century, which took the lives of three sisters and several of their children early Wednesday. Jane Roh, spokesperson for District Attorney Larry Krasner, confirmed the contents of the search warrant, which was first reported by The Philadelphia Inquirer. Fire officials provided few details at an afternoon news briefing, declining to say how many people escaped the blaze or speculate on a possible cause, adding the fire scene was complex. Officials also did not say where the fire began, calling it part of the investigation. “I …