I taught three students that together went on to commit at least one at least locally high-profile murder, and probably others, and will likely die in prison as a result of them.
Two of them are brothers, Adam and Brian.
It became apparent pretty early on that their house had drug issues, and there was some serious neglect going on. Physical abuse, too, from little things the boys let slip. They rarely had lunches, never had winter coats, and their shoes regularly were being glued or duct taped together. They'd talk about fights at their house, drug use, drunk parents, all sorts of things. We reported everything the entire year they were in my classroom, trying to get some intervention (they were actually from a fairly large family, six or seven kids) but it never turned in to anything. As students, they were entitled and did things like cutting in lines, or taking someone else's candy, and rowdy, but not entirely stupid. I think the total lack of discipline at home, never having consequences for not doing homework, was a huge contributing factor to how they ended up.
Adam was not the brightest bulb. He was a follower, for sure, and a little bit of a bully. He'd posture to show off, but if you pressed him, he'd back down. Never had problems with him in the classroom, after the first week, just in the halls, or recess, or at the bus stops. Acted tough, but at least when I knew him, it was a fairly unconvincing act.
Brian was always kind, when neither of the other two co-murderers were around. A really quiet kid, a thinker. But he stuck by his brother like glue. I guess they didn't have much else going for them, nobody else to watch their backs, so they were 100% together in pretty much everything. I really hoped Brian'd end up in a better place. He was brighter, kinder, and patient. Liked to read. I had hope, with him. I thought, if any of them have a chance, it's him.
And if it weren't for the third kid they fell in with, Carl, he probably would have.
Carl was a problem kid, had a file thicker than a dictionary. I saw him stab a kid, for no reason, and then say it was because he wanted to see what happened. We had to remove all scissors from our classroom because he liked to cut things. He threw a desk, once. Mid-story time, no apparent trigger. Just got up, threw it at a girl, and then laughed when she started crying.
He was a nightmare on the bus, on the playground, and so on. He had a recess duty assigned to keep an eye on him, because whether he directly did it or not, kids got hurt when he was around. He talked about killing animals, going hunting, and about doing things like taking people into the woods, getting them really lost, and then leaving them to die. He was a creep. He liked to pick on little girls. Not the ones in his grade, but ones 4 – 5 years younger. He'd corner them and bully them to tears, sometimes physically snatching at their dresses, or pulling their hair. He was awful, and constantly in and out of the principal's office.
Adam worshiped Carl, or followed him around like it, anyway, and Brian, well, he stuck with his brother. It was so sad to see happening. They all lived in the same area, and knew one another outside of school, and I always got the impression that Brian was afraid of Carl.
I know some of the other teachers in the building were. Hell, I'll even admit I was, too. I was on constant guard with him in class. He even in elementary school was fully capable of doing some serious permanent harm, and we all knew it.
Together, while still in high school, they abducted and killed a classmate.