A&E had a true crime show called "Cold Case" and this was one of the cases that they profiled. A chat board on the A&E website started up around the TV series. They were scattered all across the country, but for some reason that community latched onto this case and started doing the armchair sleuthing. Some pro boards started up out of that group, and then a Los Angeles magazine writer, Michelle McNamara, came along. She's the one who came up with the phrase "Golden State Killer” around 2011.

Source: Los Angeles Times June 11, 2019 10:30 UTC