I went to high school with a guy who accidentally killed 2 people a few years later. He was a year younger than me but we had mutual friends and got along pretty well. We weren't super close but hung out with moderate frequency, especially after high school. He was a really really smart, nice kid.
He always had an interest in psychedelics and eventually took to cooking up his own. He made a bad batch of synthetic acid, 2C-E if I recall correctly, in college that ended up killing two teenagers. Really sad stuff. Lots of young lives ruined and families hurt.
He's still in federal prison and will be until he's about 40.