The attacker(s) will be prosecuted, as they should be because this attack is wrong on many levels. This is very common for anti-Muslim attackers in the western world.

In the middle east, Christian killings based on religion is common in many areas, and is sometimes sanctioned by the state. These killings, when not sanctioned by the state are often not prosecuted/punished.

When there is a mass shooting in the States, it is frequently advocated that stricter gun laws are necessary. The gun laws are already very strict in New Zealand, including the requirement to hold a license to be in possession of a gun, Gun sellers must be licensed, and background checks are mandatory for everyone applying for a license (you must pass a background check before the first time you buy a gun), and licenses can be revoked easily by the police.