Well, we don't know enough about this case to really judge it. But my key take away is NOT that this kid is a future murderer, but rather the opposite, that internet harassment is something very different than real harassment, something normal people can get into, somewhere where it's too easy to disconnect emotionally from the target and the suffering of the target. The kid may not have been able to visualize the suffering that he caused, getting de-sensitized to the words and images used in the harassment (you don't need to stay long in 4chan for that to happen).
Of course, it doesn't make it more ok, it just means we shouldn't use the same ruler to measure internet harassment as real harassment.
How do you reckon what's described in this article doesn't count as “real” harassment? Just because the harassment is done anonymously online doesn't mean it's any easier to deal with, perhaps even the opposite. Not to mention the dead flowers and the other things which happened outside the web.
In the end I believe the internet just provides an easier way of stalking people than through the traditional means, but the victims are affected just as badly, so I don't think you shouldn't take internet harassment any more lightly.