Some American opponents of Abdelbaset Ali Mohmed al Megrahi’s release have said that over there Megrahi would have been sentenced to death. By now he might be dead, not through prostate cancer but by lethal injection. The same people would argue that Lockerbie shows why the death penalty is an appropriate punishment. Megrahi’s execution, they’d say, would be a “humane”, controlled extinguishing of life, “balancing out” the heinous act of cold-bloodedly killing 270 people.

This is totally wrong. Megrahi’s guilt is considered certain by some but extremely dubious by others. The case against him was largely circumstantial and itself illustrates the extent to which the need for corroboration in Scottish law has been eroded over the years. Would any legal system in the world feel justified in carrying out an execution in these circumstances?

This is the “pragmatic” anti-death penalty argument. It’s rare that you can be 100% certain you’ve convicted the right person. Even confessions may stem from delusion or police coercion. For instance, in the past 30 years, 100-plus prisoners have been released from US death rows, some after the discovery of evidence proving their innocence. Consequently, imprisonment is the rational response to serious crime. If a miscarriage of justice is discovered, a prisoner can still walk free.

Meanwhile, there are powerful moral arguments against the death penalty. The calculated cruelty of killing someone is a gut-wrenching business. Recently I visited Japan where increasing use of capital punishment is worrying human rights groups. Last year Japan hanged 15 people – including a 75-year-old man taken to the execution chamber in a wheelchair. A condemned prisoner, a noose around their neck, is placed on a trapdoor operated by a remote-controlled system in a separate room. Three people press three separate buttons. Only one connects to the trapdoor so no-one knows whether they’ve pressed the fatal button. Even the willing executioner is insulated from the process.

Except in time of war or in self-defence, we’re rightly outraged by the bloody business of killing, but that’s no reason to replicate the act in our own justice systems. Justice should be about dispensing punishments that are sober and grave, but never cruel and vengeful. Seen this way, convicted mass killers like Megrahi aren’t any more “deserving” of death sentences than other criminals. They’re just extreme cases confirming that our justice systems need to rise above a hateful disgust for human life. Saddam

Hussein was a murderous despot but that doesn’t mean the Iraqi government had to disgrace itself with a hanging of the former dictator. Neither does it mean that Iraq should ape Saddam by recently sentencing 1000 people to death, many after unfair trials.

There’s another aspect to this. In Japan, prisoners are literally being driven insane on what is probably the world’s most draconian death row. Inmates are kept in isolation cells, forbidden from walking and must remain seated. Talking to other prisoners or even making eye contact with guards is strictly prohibited. And, astonishingly, prisoners aren’t told of their execution date until the morning itself, so they live in perpetual fear that each day could be their last.

Unsurprisingly, Japan’s death row is a morass of mental illness. One man, Hakamada Iwao, 73, has been there for an unbelievable four decades. Indeed September 11 marked exactly 41 years since his sentence, a period that Amnesty International believes makes Hakamada the world’s longest-serving death row prisoner. Additionally, his original conviction was unfair and Hakamada’s mental state is now so poor that he talks of “dragons” and is convinced that he’s immortal. Despite one psychiatrist recently saying he exists in a “state of insanity” Hakamada remains on death row and could be executed any time.

I’m not seeking to re-open the debate about Kenny MacAskill’s

decision to exercise compassion for Megrahi. Instead, with American commentators’ calls for Megrahi’s blood ringing in my ears, I want to make the simple observation that justice should always involve the exercise of restraint and humanity.

The truth is that neither a hypothetical Scottish capital court nor a US court would have been right to pass a death sentence on Megrahi. One hundred exonerated US death row prisoners is one powerful argument against that. The case of Japanese prisoner Hakamada Iwao is another.

Alistair Carmichael MP is chair of the All Party Parliamentary Group for the Abolition of the Death Penalty.