A great storm blew across Europe in 1993 and even the trees of Treblinka were torn out by their roots. The Nazis had destroyed their death camp before the arrival of the Red Army almost half a century earlier, scattering the remains of hundreds of thousands of their Jewish victims.

Now, only a series of grey stones, each marked with the town or city in which the unseen dead once lived, lay across the site, along with candles and – after the tempest – a litter of uprooted trees. I wandered across and looked at the upturned roots. There were tiny fragments of bone in the undergrowth and in one twisted root, a human tooth; it had a dentist's filling which faintly reflected the grey Polish afternoon.

With director Michael Dutfield, I was making a film series, Beirut to Bosnia, which asked why Muslims had come to hate the West. I had traced the original home of a Palestinian exile in Beirut to Acre; here, the elderly Jewish owner – for under Israeli law, the Palestinian home was now his home – told me of his eviction from Poland and the murder of his mother in the gas chambers of Treblinka. We found his Polish house in the town of Trebinja – "are they coming back?" the woman householder asked in consternation after I knocked on the door in the desolate coal-mining town – and filmed at Treblinka where the old man's mother had been killed.

There is a bleak railway station, still with a "Treblinka" sign over the platform, and a grass-covered way where a siding once took the cattle trains of Jews into the tall trees obscuring the camp and up to the selection ramps. Even the roads we drove on to reach Treblinka were built by the Nazis. I knew all about this wickedness. Only six years earlier, in Jerusalem, I had attended part of the trial of "Ivan the Terrible", the death camp guard who had bludgeoned the Jews into the gas chambers of this awful place. Day after day, Israeli schoolchildren would be taken to the modern little courtroom in west Jerusalem where John Demjanjuk was on trial, to learn at first hand what fate the Nazis – Demjanjuk was himself a Ukrainian – had visited on the Jews of Europe.

Demjanjuk, with his piercing glasses and sharp face, looked every bit the part as witnesses stepped forward to identify him as the cruellest of their tormentors at Treblinka. His European lawyer, an Irishman who stayed at the American Colony hotel, insisted that Demjanjuk's identity card, a vital part of Israel's evidence, was a forgery.

He was a handsome man – Israeli girls swooned over him – who took his lawyer's duties as seriously as the court took their responsibility for the accused. Demjanjuk was innocent, he insisted. And, after sentencing him to death and confining him to six years in a condemned cell, the court eventually came to the same conclusion. Demjanjuk was not "Ivan the Terrible". He was sent back to America, whence he had originally been extradited. Although vital evidence had been kept from the trial judges by the Americans – and despite the fairness of the Israeli trial of an even greater monster, Adolf Eichmann, in 1962 – this was not Israel's finest hour.

So I was all the more stunned when, driving back from Treblinka to Warsaw after our 1993 film shoot – it was the same year as Demjanjuk's release – our Polish translator, a young female lawyer, asked if I had heard of the Ukrainian Nazi camp guard. Yes, I said, I had been at Demjanjuk's trial in Jerusalem. We were now travelling close to Sobibor, a brutal satellite camp of Treblinka during the Nazi occupation, and our translator suddenly remarked that "everyone round here knows Demjanjuk". I turned to her in amazement. "Yes," she said. "His then-wife lived in Sobibor, not Treblinka, and lots of people knew her and knew him. His name is very well known in Sobibor." That wonderful writer Gitta Sereny had already worked out the Sobibor connection. But here were people who actually remembered Demjanjuk.

I returned to the kidnap hell of Beirut and quickly forgot the conversation. And there I still was in the Middle East three months ago when John Demjanjuk went on trial yet again, this time in Germany and – much more to the point – for his crimes against humanity at Sobibor. No longer the sharp-faced bureaucrat-guard I had seen in Jerusalem, no longer gifted with the sobriquet of "Ivan the Terrible" (real name Ivan Marchenko), he wore large black sunglasses and sat on a hospital gurney – he was now 91 – and spoke not a word during his Munich trial.

He got a mere five years' imprisonment for complicity in the murder of 28,060 Jews at Sobibor and was allowed to go free pending his appeal. One of the very last survivors of Sobibor, 90-year old Jules Schelvis, who lost his wife and parents in the gas chambers, put a very pertinent question at the end of the trial. "Have we won or have we lost?" he asked.

Why did it take 18 years – from Jerusalem to Munich – to get Demjanjuk? I ask myself this question in Beirut where lesser criminals – responsible for perhaps a thousand deaths, maybe two thousand, in the Beirut civil war – live happily on in permanent immunity scarcely 21 years after their crimes were committed.