MARIETTA, Ga.—A convicted sex offender has been arrested more than 30 years after an 8-year-old boy was found dead in the woods of an Atlanta suburb. James Michael Coates, 56, faces multiple charges, including murder and aggravated child molestation in the 1988 killing of Joshua Harmon, Roswell police announced Friday. He was taken into custody Wednesday after a traffic stop as he rode in an Uber. Coates, of Woodstock, was arrested after DNA evidence collected from the crime scene linked him to the killing, police said. Detectives, police officers, scientists and others who worked the case over the years “never gave up hope in bringing Josh’s killer to justice,” Roswell Police Chief James Conroy said at a news conference. “This was a tragedy that no family should endure,” Conroy said. “The death of Josh and the fact that his killer remained free for such a long time is unimaginable.” “When …