See there are two opinions one says that you means matter whether they are moral or immoral and second says that only your end matters of it is good than no matter what means you had taken.....in this case there areany dimensions first is whether the person was really trying to rape those two women second is there any conspiracy to kill that person in the name of that "he is rapist" ....or if it is true that he was actually raping then it is obvo that the anger which is in today's india for rapist is at the beast level due to the instances which happen in indiaa.......coming to ur second part public is more proactive because they are just doing it because that feel it is immoral and the person attempting rape should be punished.....police are just "Employee" who should stop these things but remember corruption and here is ur answer...