Unfortunately this was bound to happen. After years of watching jihadist do the same to non-Muslims, and lack of security in places of worship, it was a matter of time a white terrorist would act upon revenge killings. All mosques should have an armed person or two casing the building.
I am not sure about the gun laws in New Zealand but in my state it is an open-carry and stand your ground state. It means I can openly carry my gun and legally shoot someone who harms my person or property.
Worst racist of them all are the eastern European block, Polish, Serbs, etc., these degenerates compete with immigrants for jobs and are compelled to act on impulses much sooner. Ever heard of eastern-Europeans giving foreign aid to 3rd world countries or concerned about global warming? Nor have I. They still carry the legacy of the Soviet Union destitution and despair.