教父2中麦克为什么一定要杀他的brother？

Micheal掐着Fredo的脖子说“I know it was you,fredo,you broke my heart”，这里Michael得知是Fredo勾结外人应该是从party一开始的时候,Fredo向其他客人卖弄时说:"是强尼(罗斯的手下)告诉我的,他曾带我来此,百闻不如一见,是吧?没有一个罗斯的人能像强尼一样,这么了解此地呀!"而这之前,Fredo居然假装与强尼初次见面,这才使得Michael了解到家族中的叛徒就是Fredo.

如果大家还有印象的话,应该不会忘了The Godfather1中,Michael去和Moe Greene谈生意时,曾嘱咐过Fredo:"Fredo -- you're my older brother, and I love you. But don't ever take sides with anyone against the Family again. Ever."

Fredo---Michael曾经认为生性并不聪明但却深爱家族的人,他的亲兄弟,却一而再,再而三地勾结外人,使家族一度差点瓦解....

So what can Michael do....As a Godfather?.....

Fredo broke Michael's heart again and again.And he would destroy the Corleone Family sooner or later,if didn't let him rest...

But as a little brother or a ordinary man.....

Michael was so sorrow.....that he penanced with tears when he was old."I killed my mother's son....I killed my father's son.."