A fourth person has been arrested and charged with the murder of Naod Welday, 18, at the Mount Olympus trailhead on Aug. 3. Christian De La Rosa, 17, will be charged as an adult and is accused of first-degree murder, aggravated kidnapping, firearms charges and assault, all with gang enhancements. He joins the list of those accused of the killings that includes 21-year-old Mateo Heriberto Martinez, Alex Daniel Ruiz Martinez, 19, and a 15-year-old who has not been named.