Just hang them
We seem to have become sidetracked into a discussion of the punishment component of a sentence, presumably triggered by my putdown of the standard argument for executions (well, aside from the financial one, which others have dealt with). Some thoughts: Without a punishment part, there ceases to be a deterrent. Fines become unworkable since the necessary value of one would hopelessly bankrupt a convict as you move up the scale of seriousness - which isn't going to produce a more well-rounded person. Some element of punishment is often an unpleasant necessity and we should not buck away from it just because we'd rather avoid it. In many cases involving serious or violent crime, punishment ceases to be an issue since the necessary rehabilitation time is far in excess anyway.
However, the present situation is such that all we really have from prison is punishment and protection of the public. Punishment should generally be the least of all the considerations in a sentence, but it is currently the main. Rehabilitation is all but nonexistent in most of the world. To give examples I am familiar with, look at the cut of funding to HMP Grendon (the one and only rehabilitation prison in England and Wales) or, going further back, the closure of Special Unit at HMP Barlinnie, a smaller-scale scheme with similar aims in Scotland. Anybody with a non-life sentence is in jail purely for punishment with very few exceptions, and that is unjustifiable.
The release of Abdelbaset Ali Mohmed al-Megrahi (no, I didn't have to look up his name) should have no bearing on your views on reform since - making the controversial assumption the conviction itself was correct or at least irrelevant - the cited reason was compassion for a dying man. Anybody who wishes to discuss the validity of such should not be tackling the decision itself, but rather the legislation as it stands: predictions of death are not an exact science - how long is Hawking overdue? Compassion is utterly vital, but the debate that should have and has never happened is how to go forward on that with such margins of uncertainty.
As a side note, a difficult problem is measuring reform, though it is not insurmountable and, indeed, it is supposedly already done for those by parole boards reviewing indefinite sentences once the minimum term has passed. As in to how it works currently I have no idea; just how the conditions of decades as a prisoner in Category A or B (or equivalent) prison are supposed to reform anyone is beyond me.
Regarding assisted suicide, I'd rather the scheme for those with illness or infirmity etc be entirely separate from any scheme for longterm prisoners.
One case I'd point at, whilst we are on the subject, is an Amerikan who killed another inmate because he wanted to die and the only method available was the death penalty. I would class that as a suicide as much as an execution.