The first was more of a theory that linked together over 40 murders, and that was the Smiley Face Murders.
Now, there is a lot of controversy surrounding this theory, yet there is FAR too much evidence linking the 45 murders for it to be a coincidence.
Beginning in the late 1990s and spanning to the 2010s, 45 young men were found dead in bodies of water across multiple Midwestern American states.
Investigations quickly ruled out the possibility of accidental drowning. Instead, it was concluded by not one but multiple Law enforcement agencies that corpses were murder victims.
I first heard about this case when I was in high school, as one of the many online forums I frequented continuously brought the topic up, causing my interest to peak.