Catching someone who has committed a crime and bringing them to justice is one thing, stopping someone who has caused intentional killing and has himself proclaimed his intent to cause more killings, and urges others to do the same is entirely something else.

The former may be a case for the judiciary. The latter is a case for pragmatic self-defense, not morals, not principles, not law, not Registered Letters.

If someone has killed your mother, has declared his intent to kill your whole family, then friends, then acquaintances, etc., whatcha gonna do?