Golden State Killer was one of the most heinous criminals of the last century. After decades long investigation at last he was arrested. You may wonder why law-enforcement took that much time to bring the criminal to justice.
Two points to consider here: his work experience and lack of technology. The criminal not only served as a police officer but was also a war veteran from U.S. Navy. On April 24, 2018 the killer was arrested at age of 72 and still waiting to hear the final sentence. It is taking so long due to his long list of crimes.
Joseph James DeAngelo Jr. is charged with 13 murders, more than 50 rapes, and over 100 burglaries in California between 1974 and 1986. He was responsible for at least three crime sprees throughout California.
His first series of crimes started at Visalia, California from 1973 to 1976. He was married to Sharon Marie Huddle in November 1973. At that time he was a burglary unit police officer in Exeter - a town of about 5,000 people, near Visalia. Over a period of 20 months, DeAngelo is believed to have been responsible for one murder and around 120 burglaries. His activities got him a nickname - 'Visalia Ransacker'.
East Area Rapist
Then he moved to Auburn and served the police department from August 1976 to July 1979. In this span DeAngelo progressed from burglary to rape. He used to stalk middle-class neighborhoods at night in search of women who were alone. DeAngelo sometimes spent hours in the home ransacking, eating food, drinking beer. During this period he raped 50 women and he was named - 'East Area Rapist'.
Original Night Stalker
In 1979 DeAngelo moved to southern California and began killing his victims. The attacks lasted until 1981. Only the couple in the first attack survived, alerting neighbors and forcing the intruder to flee; the other victims were murdered by gunshot or bludgeoning. During this period he committed at least 13 murders. These crimes gave him a nickname too - 'Original Night Stalker' as another serial killer Richard Ramirez was named 'Night Stalker'.
In 2001 somehow law-officials were able to connect Original Night Stalker to the East Area Rapist. But still DeAngelo was out of the picture. Investigation was ongoing but progress was none. Another decade passed and the victims almost lost their hope. To heighten awareness of the case, crime writer Michelle McNamara coined the name 'Golden State Killer' in early 2013.
The Federal Bureau of Investigation (FBI) and local law-enforcement agencies held a news conference on June 15, 2016, to announce a renewed nationwide effort, offering a $50,000 reward for his capture. On April 24, 2018, authorities charged 72-year-old DeAngelo with eight counts of first-degree murder, based upon DNA evidence.
The investigations were failing before due to lack of technology to match DNA evidences. But technical advancement of last decade helps FBI to solve this puzzle. When asked about the details of this impossible investigation, FBI stated,
Through the use of genetic genealogy searching on GEDmatch, investigators identified distant relatives of DeAngelo - including family members directly related to his great-great-great-great grandfather dating back to the 1800s. Based on this information, investigators built about 25 different family trees. The tree that eventually linked to DeAngelo alone contained approximately 1,000 people. Over the course of a few months, investigators used other clues like age, sex and place of residence to rule out suspects populating these trees, eliminating suspects one by one until only DeAngelo remained.