Then sending them to death is the right choice because the propability that they will go out of prison and redo what they did before will be eliminated.
Some people who say rapists are rapists then even sending them to life in prison is still merciful compared to death and also there is no life in prison which is perfectly excuted, some of these who are sent to life in prison will go out after 20 or 30 or 40 years so when they go out there will be some of them who will not redo what they did before but some might redo what they did before so the possibility to get one person of the community affected badly is there.
Last thing to say sending to death guilty murderers will safe innocents.