The death toll in the country's worst massacre rose to 13 Thursday when police found human remains in the debris of a house the killer set ablaze before opening fire on his neighbors.

The remains were believed to be those of two 11-year-old girls missing in the 23-hour siege that ended Wednesday the South Island seaside hamlet of Aramoana.Discovery of the two bodies raised to 13 the number of people slain by 33-year-old David Gray before police killed him in a shootout. Two children were wounded by Gray, who wiped out nearly half of Aramoana's population.

Gray began his killing spree Tuesday night by setting a neighbor's house on fire, then opening fire on people who arrived to try to extinguish the blaze. The motive for his actions remains unclear.

Police kept the town cordoned off Thursday except for forensic experts, government officials and journalists.

Gray, who holed up in his home before fleeing to a house on the edge of town, used high-powered rifles to shoot neighbors and keep police from reaching victims scattered on the lawn of his house and a nearby street.