Police in Washington state are searching for a man who kidnapped and murdered his three young girls.Olivia, five, Evelyn, eight, and Paityn, nine, were found dead on Sunday, three days after a planned visitation with their father, 32-year-old Travis Decker.According to the Wenatchee Police Department, the girls' mother called 911 after her daughters were not returned by Decker on the evening of May 30. Officers immediately began tracking his white 2017 GMC Sierra — out of which he had been living — and searched nearby motels.Authorities considered sending out an AMBER Alert, but determined that it "did not meet the required criteria." Instead, an Endangered Missing Person Alert was issued. Search efforts continued throughout the weekend with assistance from the Federal Bureau of Investigations and the Chelan County Sheriff's Office..On Monday afternoon, Decker's unoccupied vehicle was spotted with two bloody handprints near the Rock Island Campground near Leavenworth. Backup was called in, and the ensuing search culminated in the discovery of the three missing girls. A preliminary examination determined the causes of death to be asphyxiation.Decker's charges were subsequently upgraded from three counts of first-degree custodial interference to three counts of first-degree kidnapping and three counts of first-degree murder."Decker is former military with extensive training," the WPD wrote in a statement. "It is unknown whether Decker is currently armed, but he may pose a significant risk, if approached. Any member of the public who believes they may have seen Decker since Friday May 30, and/or know his current whereabouts are asked to call 911 immediately.".According to FOX 13, Decker had a history of mental health issues, including unmedicated borderline personality disorder. When he and his wife divorced, his visitation rights were supposed to hinge on him seeking mental health treatment and anger management counselling, however he refused to sign off on that.