A house fire in Quakertown, Pennsylvania tragically took the lives of a father, his two young sons, and two family dogs early Christmas morning. When firefighters arrived on the scene after 1 a.m., the house was engulfed in flames so intense that first responders couldn’t safely access the residence to extinguish the blaze.

As reported by CNN, the five members of the King family were asleep inside. The mother and oldest son escaped without major injuries, but the bodies of Eric King, 41, and two children, ages 8 and 11, were discovered later on the second floor of the home. The local school district identified the children who died as Liam, a fifth-grader, and Patrick, a third-grader, according to NBC10 Philadelphia.

Investigators believe that electrical issues likely caused the Christmas tree to ignite and engulf the house in flames. “The area of origin was a Christmas tree, so we’re not sure if it’s because of electric or a dried up old Christmas tree,” Quakertown Fire Marshal Doug Wilhelm told CNN.