Two former Roxbury men have been indicted in the 2010 slaying of 18-year-old Terrence Kelley, who was chased and gunned down in Boston’s Grove Hall section, the Suffolk district attorney’s office said. The indictment charged Darius Gibson, 22, with murder, unlawful possession of a firearm, and witness intimidation. On Oct. 17, James Austin, 24, was indicted on charges of misleading police in the investigation and being an accessory after Kelley’s slaying, prosecutors said. Both men are already detained on other matters. Kelley’s death was part of a series of separate gang-related shootings in the Grove Hall area in 2010.