I can guarantee you a bullet to the head is much more cheaper and if we speed up the process for people who are clearly guilty and have overwhelming proof that they are guilty then we’d save a lot of money than feeding, housing and caring for them for a lifetime.
You can’t just say we should speed up the process and expect it to be sped up. Crime isn’t clear, and proceedings must be thorough. Even still, there is no moral justification for ending someone’s life if they are detained and no longer a threat. It’s just a barbaric impulse to want to kill someone even though they can’t do any more damage. If a practice can’t justify itself, then it should be dismantled.