Six people were killed and two others injured Sunday night in Napa County when a minivan veered off the road and slammed into a tree, authorities said. The driver, later arrested on suspicion of DUI and murder, was among the survivors, according to the California Highway Patrol. The CHP and Napa County Sheriff's deputies responded about 5:50 p.m. to the single-vehicle crash off Pope Valley Road north of Howell Mountain Road.