Puppy trying to kill another one.

One puppy is trying to kill his sibling. The other one is very weak and the strong oneis repeatedly crushing his neck and dragging him harshly. I have saved him 3 times but he is not stopping whenever he gets the chance. I thought it is temporary and will stop as he will get tired. But he is not stopping from yesterday night . I am sure it isn't just a playful act but he is seriously being very aggressive. Both are Indies (street one only ) , I was looking after them they are mostly of 2 3 month's.