I suspect you are just a troll as others have said, but in the case you aren't;

It's been shown for all crimes, that degree of punishment doesn't really have much effect on deterrence. People tend to not know what the punishment for any given crime is, they tend to underestimate how likely they are to get caught, and when worrying about consequences they tend to worry about consequences they understand, like how their family or friends will react, not what living in prison for years will be like.

The justice system everywhere is fallible, protections for those in jail aren't only for the absolutely guilty, they are for the innocent who are incorrectly incarcerated.

Killing someone wont undue what they've done. As horrific as it is, the trauma inflicted on someone can't be undone. You are only putting more suffering into the world when you punish someone without tangible goals.