Sadly these sort of attacks are pretty hard to prevent, you can remain vigilant and raid suspected houses but they only have to get lucky once whereas you have to be lucky all the time.
The anti-migrant parties will make hay from this, no mistake, they will do well and gain more followers out of it.

In fact, they are probably the only people who benefit from attacks like this.
Anyway, that's enough of that talk from me, this is not really the time for it, and I apologise for branching off into it. For now, all we can do is watch and hope that this situation is resolved quickly and with as few casualties as possible.