Look, of course gay kids, along with anyone outside the norms are harassed in school. Most kids are outside the norms at some point.
But this documentary literally inverts the harrassment. In this case a 15 year old was, on a near daily basis sexually harassing a 13 year old (who had just turned 14 when the shooting took place) . And after complaining to school authorities teachers etc, and getting nowhere in stopping the harassment, the younger kid being harassed finally took maters in his own hands.
We have to ask ourselves how we would feel if a 15 year old boy was sexually harassing a 13-year-old girl regularly and school authorities did nothing. Of course the younger kid was not justified in killing his tormentor. But those are mitigating facts and an important part of the context.