ludwig - an interesting ethical dilema.
My personal perspective is that it is fundamentally wrong to take the life of someone in punishment for taking another life - it simply reduces the state to the status of the criminal, without the benefit of extenuating circumstances, repellent though those may be. To take a life in cold blood - to employ a person or persons to take the life of someone as a profession is to be the very worst example of cynical vengence, and has no place in a civilised society.
That said - such crimes must be dealt with in a way that sends a message to the perpetrator, and to society as a whole. That is the removal of the individual from the society they have refused to live in normally - combined with the loss of any identity and freedom. This provides the twin aspects of the removal of the chance for re-offending, thus avoiding putting lives at risk, together with a message -albeit often unheard - that society will not tolerate such behaviours, and there is a legal system in place to keep soceity safe, as far as is possible.
As I have opined at length on this thread, I cannot see execution as anything by state-sponsored murder, and the emotional righteous anger of a vociforous few who claim they would 'pull the lever', or 'leave him with the other prisoners' etc. ad nauseum, does not justify it.
It is very easy to allow emotions to run away with us in cases like this, where a child has died violently, but who could honestly - and I mean really honestly - live with themselves once that righteous rage has dissipated, but the vengence murder committed, or faciliated - remains in the memory for ever.
Execution is not simply a matter of 'saving the tax payers' money' - in fact, it is not a simple matter at all.