“20/20” (10 p.m., ABC): Last week Joseph DeAngelo, the suspected Golden State Killer, was arrested and charged with eight counts of first-degree murder decades after his alleged reign of terror. Tonight, correspondent Whit Johnson explores DeAngelo’s background, questions how the Golden State Killer was able to elude authorities for so long and reports on how the suspect was finally tracked down. The hour also features interviews with Golden State Killer attack survivors Jane Carson-Sandler and Margaret Wardlow, and with investigator Paul Holes, who claims to have uploaded DNA information to the genetic genealogy website GEDmatch that cracked the case. It had been obtained from a duplicate rape kit collected at the Charlene Smith crime scene and kept in a freezer for 38 years. Additional interviews include Jennifer Carole, whose father Lyman Smith and stepmother Charlene were murder victims of the Golden State Killer; Michael Bowker, a magazine writer who was briefly a suspect before being cleared by authorities; William and Joan Oakley, neighbors