When you're a hero you know what you're signing up for, there was an idea that side kicks were held to a moral compass by villains that you didn't hurt them because they were children. But not with the Joker, he did not have that morality....and it's what cost his second robins life. Beaten to a pulp and then blown up and there's nothing Batman could do to save Jason Todd

Years later after Tim became the third Robin there were rumors of a new rogue in Gotham.