Whilst there is corruption and dishonesty in the world, the death penalty cannot be an option - ever.
Politicians, judiciary, police - all have dishonest elements and all are based on the system of democracy and capitalism.
Whilst idividuals are driven to achieve and get more for themselves; innocents will be convicted - at whatever level of crime. Problem is: you can't give life back, - you CAN however compensate for loss of freedom. (Though it is not possible to compensate for years of loss of freedom).
Until we have a political system that can be trusted, how can you trust what the government departments say and do? (And yes, the courts ARE really government controlled 'departments').
IF, and I MEAN IF, I was absolutely 100% sure of the fact that a killer intended the murder, THEN I would agree with 'a life for a life', but even this will have mitigating circumstances sometimes. (If a father kills his daughter's rapist/murderer intentionally - this is murder).
Problem is, no-one can EVER be sure, and even the best intentions have resulted in innocents being murdered through law.
If you want the death-penalty, then move to the States - some people have no hesitation in killing people for votes.