(Portland, OR)  --  Police are searching for two drivers accused of running over a pedestrian, killing him and then continuing on their way.  Police say 24-year-old Uriel Santiago-Sarabia was walking across the Tualatin Valley Highway between Southwest 160th Avenue and Southwest 170th Avenue yesterday morning when a driver struck him.  When the driver pulled over to offer help, two other vehicles struck the pedestrian and then kept going.  Santiago-Sarabia was pronounced dead at the scene.