John Demjanjuk should not be on trial

Today's Guardian carries a harrowing account of events at the Sobibor death camp in Poland in 1943, which are central to the trial in Munich of 89-year-old John Demjanjuk, accused of complicity in mass murder there. But should he be on trial at all?

My opinion is an unenthusiastic "no". The enormity of what he is accused of doing is not in dispute. Perhaps like you I have had a fairly clear understanding of what went on in the Nazi concentration camps for most of my life, at least for 50 years.

Committing mass murder on an industrial scale at the height of a great war that the Germans were busy losing, all in pursuit of a demented ideology of racial purity, makes the Holocaust – not confined to Jews – a uniquely desolate stain on humanity.

Stalin's barbaric slaughter, which old lefties are always trying to explain away, can be marked down a notch because "enemies of the people" were usually killed for what they had allegedly done, not merely for who they were.

The Rwandan genocide (and plenty like it) fit the Nazi template, but there had been no Rwandan Beethoven or Schiller. The Atlantic slave trade? Far from unique either – very horrible – but it was instrumental. Slaves weren't shipped to the Americas to be killed as Nazi victims were to Sobibor – though millions were killed – but to work.

Economics drove the slave trade; racial theories were merely used to justify it. It was always opposed.

So string up Demjanjuk? That's what the Israelis tried to do when he first went on trial in Jerusalem in 1988. Yes, this affair has been going on for decades. Just flick through the Wikipedia file. His original conviction was overturned by the Israeli supreme court – surely an act of moral courage – in 1993 because of evidential doubts that Demjanjuk really was the notorious camp guard known as "Ivan the Terrible".

That's hardly surprising, is it? Most witnesses to his alleged crimes are – by definition – dead, the survivors old and infirm, like the accused, whose appearance in court on a stretcher is, like his wheelchair and other props, suspected by some of being a fraud.

How can we tell? It's easy to imagine the health issue both ways, though not the defence's familiar claim that their Ukrainian-born, naturalised American (citizenship later revoked) client is a victim too – caught between the 20th century's rival totalitarian ideologies and forced into complicity with their crimes.

Times columnist Danny Finkelstein, makes short work of that line of argument today, the flawed "situationist" view that suggests that human beings adapt to the situation in which they find themselves, as evidenced by Stanley Milgram's famous torture tests at Yale in 1961.

As part of what was actually a fake "experiment" to test pain levels, his volunteers kept administering ever-stronger electric shocks despite the fact that they could see that the "patients" (actually actors) were screaming.

Plenty of potential camp guards in the Yale area, he concluded.

As I type I'm listening to a young Muslim puritan from Luton on Radio 4.

I wouldn't want him too near the electricity switch either. We all know people – from the very damaged to the very cold and cerebral – who we suspect would readily do us harm to further a bad cause.

Finkelstein is right to argue that "whatever their nature or circumstances, human beings retain a moral choice". That's what we have to cling to, right? But that goes for the rest of us too.

This man has been tried and the evidence found wanting. He's been reviled and disowned. He's ended up in a German courtroom because no one else would take him. Won't that do for one lifetime? He was, by any test, a very small cog in the machinery of evil, the most junior person to have been tried by anti-Nazi courts.

We went through all this in Britain 20 years ago when Margaret Thatcher insisted on pushing through what became the 1991 War Crimes Act against the advice of the Lords, who had seen enough of the second world war at first hand – at a time when the average MP had been six in 1939 – to want to call it a day. One person, Anthony Sawoniuk, was convicted as a result. Sentenced to life imprisonment in 2005 he died in jail.

Many people – including me – like the old saying about "the mill of God grinding slow, but exceeding fine" and the idea behind it that bad deeds will catch up with people in the end. But the mill of man's law courts are a different matter.

By now we all know what happened in the camps. I recently read Maus, Art Spiegelman's brilliant cartoon biography of his father, and was surprised to be moved to tears all over again. But there are plenty of bad things that we can try to do something about going on in the world of today rather than weep again for the likes of Sobibor.