The search continued Monday for vandals who targeted four power substations on Christmas Day in Pierce County, Washington, setting fire to at least one of the facilities and knocking out power to more than 14,000 utility customers, authorities said.The vandalism came amid a string of similar sabotage incidents across the country, including several in the Northwest, and follows a bulletin issued last month by the U.S. Department of Homeland Security warning that critical infrastructure could be among the targets of possible attacks by "lone offenders and small groups motivated by a range of ideological beliefs and/or personal grievances."In all four episodes, the saboteurs broke into the fenced-off power stations and deliberately damaged equipment, according to the sheriff's office.Officials initially said three power stations were vandalized, but early Monday morning they said a fourth substation was damaged in a deliberately caused fire near the city of Graham, cutting power to homes in Kapowsin and Graham."We know this incident has impacted many people’s holiday celebrations, and our crews are working hard to get power safely restored to all customers as quickly as we can," it added."