There's a full range of possible depictions on the scale from "pretending" murder is G-rated to showing gratuitous violence and unnecessary gory detail.

For example, it's largely sufficient to the plot and character development to know that Batman's parents were killed by a mugger when Bruce was just a boy, and that Uncle Ben was killed by a petty criminal whom Spiderman had the chance to apprehend (but declined to do so). Nothing is added by showing entry/exit wounds, slow pans over puddles of and spurts of blood, or any other sort of gore porn.