>> 59-year-old rex heuermann is believed to be responsible for murdering four women. >> suspected serial killer has been arraigned. >> this is the kind of case a prosecutor wants. >> the cell phone records. the computer searches. the dna recovered from the scene. very strong evidence to prosecute this case. >> so it's a real triumph of law enforcement. >> what you're looking at is a new genre of investigation. because it combines classic detective work. shoe leather, door knocking. finding witnesses. finding little connection with technology. >> even the most careful killer really can't hide forever. >> technology will catch up and new analysis methods come on line and that's why we hold on to evidence for a long time. ♪ >> coming up, the victims' families. >> this is the last place she