The Swedish police and media have been restrictive with details to prevent the spread of rumors and premature speculation. The motive is not yet clear.
I believe I've kept my speculation above to a minimum and only to what someone with local Swedish knowledge would immediately infer from the sparse information provided. Here's why:
1. When I hear "school shooting", I think of a teenager shooting up a middle school, which would represent a worrying and sudden shift in how Swedish society operates.
2. When I hear about a mass murder in Europe, I worry that it's going to be a demonstration by someone like ISIS (which is 99% eliminated, but not 100%) that they have reach into the core of Western populations. An attack like that might mean that the US will be triggered to do something disproportionate to some unrelated country.
3. If not those two things, it could have been an escalation in gang violence.
The intitial reports said nothing direct to eliminate these possible meanings, but from the indirect information, it's neither of those things. The release of the attacker's identity confirms it, he's a 35-year old man of Swedish heritage who used to go to the school, not a kid, not a jihadist, not someone unrelated to the school.
What's new for Sweden is the horrifying magnitude of the attack.