You can prove bullying. And that should be covered by harassment legislation. You cannot prove bullying caused suicide. I am not saying it doesn't, because I think it can. However, the suicide is not solely as a result of the bullying.
There are other factors that play a significant role, so what would this crime be? It can't be manslaughter. Would it be a new offence? What would the criteria be?
I just picture myself as an juror and I would never be able to able to convict, I cannot imagine any amount of evidence that would convince me that someone killed themselves exclusively as a result of the bullying.