Rosa, you used the word "justify" which requires a concept of justice in order to function.
As should be obvious, neither of the historical murder examples you gave justify murder. The first is predicated on the belief that killing Hitler is justified, the second that the life of 3000 Jews is worth the life of one priest (and the belief that killing the shepherd will save the flock). All of these precepts are open to debate, historical or not. (I shouldn't have to point out that we don't know if killing Hitler would have stemmed the Holocaust, or if killing the pastor would have saved the Jews, who apparently survived nonetheless.)
Any such questions contain cultural assumptions that disguise greater political ends. As such, they are tyrannical, and should be eradicated. Like Hitler and your priest.