Agree with that Joeluke, they should all be hanged and there should be no Queen's mercy and leniency allowed. Miscarriages of justice in murders is , thankfully, rare. When it happens the deceased's estate, their family, should sue and be compensated for the death, as happens in other cases where someone has been killed because of the negligence of another.
That's fine but it never has happened. One hundred per cent of convicted murderers were not hanged. They escaped by the Queen (the Home Secretary on her behalf) granting leniency or, later, because the murder was not one which attracted the death penalty. Back in the 1930s I believe, no more than two thirds were hanged but, looking back, some of those hanged deserved leniency.
But I am not sure that the death penalty would reduce the number of murderers; that's because murderers don't contemplate the consequences.