West Memphis Three
Satanic ritual rape and killing of two male children. Subsequent investigations damn well proved these three boys did it. Hollywood swooped in to defend them.

It was 3 kids, and while the three's guilt is one of the two (competing) semi-official theories, I suspect there was something much deeper at work. I think half the area was involved with that cult. Echols himself initially told police there was a huge satanist presence in West Memphis, including adults.

One thing I find interesting is how these guys were an early manifestation of the "Trench Coat Mafia" clique that would be implicated in several later school shootings - Pearl, MS, Paducah, KY, and of course Columbine High School, where eyewitnesses reported multiple gunmen yet the authorities concluded it was only the two. And similarly, authorities knew that Pearl and Paducah were conspiracies, there were even indictments, convictions, etc. yet nowadays they almost never include that aspect of the event in the mainstream treatments. Ever since Pearl, Paducah, Columbine, etc. it's been the "lone nut" profile, with no discussion of other parties involved. But from a profiling perspective, how could / why would the phenomena "morph" like that? The copycat effect? Or did the people steering these massacres just get better at covering their tracks?

Interestingly, there was one other case - Mar. 1998, the massacre outside Westsides Middle School in Jonesboro, Arkansas, not too far from West Memphis! In fact, Echols and Baldwin were tried and convicted in Jonesboro in 1994, 4 years before the massacre, and Echols' public defender was Val Price, who later represented one of the two child-shooters. Because of their ages (both younger than 13), they were eventually released despite killing five people. Not too long ago, one of them, Andrew Golden, died in a fiery car 'accident' killing himself and his family. The other, Mitchell Johnson, stands as the only known mass shooter to walk free.