In the case of terrorists I don't think that the death penalty would be a deterrent as they believe in an afterlife where all good things will come to them.One example is the suicide bombers.
Of course, hanging them would mean no compensation needed if they were exonerated but had gone mad from 23 hours a day of solitary. And our marvellous coppers, not one of them, would ever actively fit someone up.
Hazi 19:41. Are you suggesting that drowning children who are on dingies with their parents would be better than bringing adults (who have committed no crimes) to 'justice'?