The prophet salla Allahu alaihi wa sallam was asked: if a person wants to take my money, should I give to him? the Prophet salla Allahu alaihi wa sallam answered: No.
The man said: what about if he fights me for it? the Prophet said: fight him
The man said: what if he kills me? The Prophet said: you are in Paradise.
The man said: what if I kill him? The Prophet said: he is in hell.
Having said this, it is not permissible to kill him without trying to stop his aggression bit by bit. One should shoot him for example in the leg rather than shooting him between the eye
And Allah knows best