Zodiac

https://en.wikipedia.org/wiki/Grim_Sleeper
https://www.ranker.com/list/serial-killers-who-were-never-caught/ranker-crime
https://en.wikipedia.org/wiki/Atlanta_Ripper
https://en.wikipedia.org/wiki/Stoneman
http://www.history.com/news/the-zodiac-killer-a-timeline
http://www.history.com/news/the-zodiac-killer-a-timeline
https://en.wikisource.org/wiki/Zodiac_Killer_letters
https://en.wikipedia.org/wiki/Paul_Avery
http://www.history.com/news/history-lists/could-any-of-these-men-have-been-the-zodiac-killer
https://www.quora.com/Why-couldnt-we-find-the-zodiac-killer
https://www.smh.com.au/national/dave-toschi-who-hunted-and-was-haunted-by-the-zodiac-serial-killer-dies-at-86-20180112-h0h8oa.html
http://www.chicagotribune.com/news/nationworld/ct-zodiac-killer-detective-dead-20180110-story.html