I think that in some cases capital punishment can be justified very easily, but how do you make the law work? For example if someone shot a burglar they could be charged with murder then in theory subject to capital punishment, yet most people would think that's not right! I still say that it will not deter those of unsound mind.
Any trial for homicide has to be defended or suicidal maniacs would be confessing all over the place.
There are such defence arguments to Murder as Attempted Murder, Joint Enterprise, Causation, Manslaughter, Voluntary Manslaughter, Diminished Responsibility, Loss of Control, Suicide Pact, Involuntary Manslaughter, Gross Negligence Manslaughter, Medical Manslaughter, Unlawful Act Manslaughter, Encouraging or Assisting Suicide, Infanticide, Familial Deaths and Serious Physical Harm, Shaken Baby Syndrome (SBS) and Sudden Infant Death Syndrome (SIDS), and Self-defence to name but a few.
With so many avenues, any Defence Counsel worth his salt would ensure that if there was the slightest doubt of a person's guilt, he would be able to produce a lesser and non- capital result. Consequently, we would not be sending criminals to their ultimate demise on a daily basis.