The kid who lived one street over and two houses down from me killed his parents one morning. He was almost invisible in our neighborhood and I don't recall him even trying to play with us. But I felt guilty that I hadn't befriended him (I was 3 years older, which was a big barrier back then).
He rode my school bus. Quiet good-looking kid, did well enough in his freshman year, but shy or withdrawn. This was a small town, it made a big impression on me.
I felt I should have been his friend - but I'm pretty sure there was no way to help at the time.