I really don't think there are "loads" of people saying he needed to die at all. Just a few fringe wingnuts. There are many people who do not mourn him but that's different to "he needed to die".
Meanwhile, there is a group who condemn this and all murders. They largely believe the offenders in these cases should be prosecuted to deter similar actions. However, they can't find much empathy for the particular victim. This group is significantly larger. Members of this group are sometimes mistaken for members of the former group because of that noise.
A guy I've never heard of getting assassinated and it making to the top of news, while a bunch of other people cheer it on, is one input.
If I just randomly hear some guy was shot by the local schizophrenic, no I probably won't look up their videos.