forensic investigators solved a landmark cold case that could change the way police investigations are conducted. we went inside for an exclusive look at the new dna technology that led detectives to an elusive killer dubbed the grim sleeper. it was the 1980s, a serial killer was terrorizing south los angeles. most of his victims were young african-american women, some had been shot with the same .25 caliber firearm. some had been strangled. some sexually assaulted. their bodies dumped in alleys. over the years, los angeles police would follow numerous leads that went nowhere. in 1988, after eight murders and an attack on the potential ninth victim who got away, the killing stopped. then nearly 15 years later, the grim sleeper would strike again. who was he? where was he hiding? police would have to wait another two decades to find the answers. >> we have about 1 1/2 million samples stored in the laboratory.