Death penalty or life sentences are dished out based on the seriousness of the offence committed. For instance in most countries cold blooded murderers are usually given the death penalty especially when they've killed more than one victim, while people charged with manslaughter, armed robbery, kidnapping and other grievous offences can be given life sentences with or without a chance of parole.
But personally i believe, there are some crimes that the punishment is not commensurate to the weight of the crime. For instance a public office holder charge and convicted of corruption should be given a death sentence sentence so as to serve as warning to others engaging in same affairs. But it's quite unfortunate that the world we live in grants them diplomatic immunity and at most gives them certain years imprisonment or house arrest. I believe is a serious injustice to the masses who are at the recieving end of the effects of corruption of public office holders and the money siphoned which would have bettered their lives.
Quite alright some countries institute life sentence in replacement of death penalty so as to give the offenders whether public office holders or regular masses the opportunity to reflect on their lives and change while in prison but i beg to differ that this does not change them, if anything it makes criminals ruthless the more and if peradventure they are released on parole, they become more careful while still undergoing their criminal acts, thus i believe certain crimes should with the death penalty. Anybody who doesn't want to be convicted should not engage in crime. It would serve as a warning to others.