fully automatic weapons have never been illegal for civilians to own, it's just they banned the manufacture of new automatic weapons for civilian sale/transfer since 1986, so any gun manufactured and then registered before then can still be transferred on the used market, with a hefty premium of course due to the now finite supply. registered firearms dealers can still obtain new manufactured automatic weapons but they can only be transferred between licensed dealers and never sold to the general public.
so whoever was behind the shooting either has a lot of money, or has owned his fully automatic weapon since before 1986 (and the subsequent price hikes), although it's equally possible he's illegally modified a semi automatic version into fully automatic (whilst that's no mean feat it is possible, in the same way manufacturing an entire gun yourself is also possible)
that said, semi automatic weapons are far less regulated and relatively easy to come across (state dependant), and semi automatic is still extremely effective both in military and civilian contexts.
it does of course go without saying that this kind of thing would be considerably more difficult with stricter firearm control as seen in (insert european country here)
