There are many crimes, which in my view warrant capital punishment, the most obvious one being murder
I see no reason to abolishing capital punishment, when there is absolute proof of guilt, such as CCTV, multiple witnesses and the like.
However, the only alternative is surely whole life imprisonment, which sadly most countries pay lip service to.
10/15/20 years and applications are generally approved for parole. The murderer is free to enjoy the rest of his/her life (usually with social security benefits) yet the victim has nothing more.