Colombian authorities have detained the driver of an overcrowded bus that burned, killing 32 children, the local mayor said on Monday. Luz Estella Duran, mayor of the village of Foundation where Sunday's tragedy took place, said witness accounts suggest the driver may have left the vehicle running with the children on board when he descended from the bus to fill tank from a portable gas container. Another 20 children and adults suffered burns, and nine remained in a delicate state, according to the mayor. The fire occurred as the group was traveling home from an event at an evangelical church. Also Read 31 Children burned to death in Colombia bus accident President Juan Manuel Santos traveled Sunday night to the town near the Caribbean coast to pay his respects to the mostly poor families of the victims. He declared a national day of mourning. "Yesterday I saw the pain of the mothers and fathers," Santos said in an interview Monday with Blu Radio in Bogota. He called for a thorough investigation so as to avoid the repeat of such a senseless, preventable tragedy.