The reasoning is more about investigations getting better at catching murderers after their first kill, preventing them from ever becoming serial killers.

But that isn’t what’s happening. It’s a 50/50 coin toss whether someone gets caught for murder. https://www.statista.com/chart/28644/rate-of-homicides-that-go-unsolved-in-the-us/

What I’ve heard is that pollution (like lead and other chemicals) is what rotted children’s brains and made the murder rate skyrocket in the 70s, 80s, and 90s as they reached adulthood.