The words would melt a heart of stone – save for those of the Gestapo torturers upstairs. The prisoners wrote their stories, their poems, their last pre-execution laments on the walls of their cells – which you can still read in the basement of the old Nazi secret police headquarters in Cologne. I spent hours there this week, reading the names and messages.

Cut into one cell wall are written these lines, in Russian, by a young woman condemned to death, apparently a slave labourer in Cologne who had joined a resistance movement in 1944:

“Here was held in custody Vallja Baran, who was betrayed by her own Russian compatriots. My husband and I were both put away in one cell … we will be facing the gallows, my only regret is to be separated [now] from the beloved husband and the whole wide world. Oh, girls, why is our youth such a botch-up? I am now 18 years old, pregnant and would love to see my first-born child. Well, this will not be possible, I have to die.”

The cells still bear their original numbers. They are complete with the massive, heavy grey-painted doors through which the Gestapo could peer at their victims, sometimes 30 to a room intended for only two or three prisoners, so many that even the local Gestapo complained to Berlin about the overcrowding.

Walking from cell to cell, I noticed a visitors’ book lying on a table between them. And in it, this week, an American couple had written these words. “Never again means never again. From Palestine to the USA-Mexico border.”

The NS Documentation Centre of the city of Cologne was founded in 1979 and became the largest memorial site in all of Germany for the victims of the Nazis (Alamy/Oscar Gonzalez/WENN.com)

I instinctively recoiled from this trite, crude, simplistic remark. How can the human rights crimes and colonial land theft committed by the Israeli government in the occupied West Bank and the overcrowding and child-separation in the refugee camps on the US border – for I presume the recorded Gestapo complaint prompted this reference in the visitors’ book – be compared to the iniquities of Nazi Germany? There must surely be a sense of perspective, at least some reluctance before committing oneself to such comparisons, most of all here, in this place of horror.

At times, more women prisoners were held here than men. Jews were kept in these cells, German Jews, and members of the German Eidelweiss Pirates, a slightly Bohemian, songs-and-guitar anti-Nazi Jugend movement which despised the Nazis. They died here, too. They were also publicly hanged in Cologne in 1944, six of them teenagers, on Himmler’s orders.

There is a sequence of photographs, of youths ascending a scaffold, some already hanging, their necks snapped by the rope, others staring petrified at the corpses of their friends as they were carefully made to stand before their own individual noose. The gallows in the courtyard of the Gestapo headquarters at 23-25 Appellhofplatz could take seven condemned men and women at one execution session.

Was this therefore the place to compare the evil of Nazi Germany with Israeli cruelty and the racist ideology of Trump and his crackpot administration? I could sympathise with the American couple who wrote those words; they were searching for a way to express their fear of the present and their hatred of injustice. But they were making an implicit parallel between the Nazis and the Israelis. I could see how easy it would be to claim – even though the word “Israel” did not exist in their message – that their contribution in the visitors’ book was antisemitic.

Let’s return for a moment to those messages on the walls, scratched with nails, screws and fingernails, but sometimes using lipstick. Here’s another that readers are unlikely to forget, again by a woman, written in pencil in September 1944. She is a German woman. She even identifies her Gestapo torturers, underlining their names.

The building was the headquarters of the Cologne Gestapo (secret police) between December 1935 and March 1945 (Alamy/Oscar Gonzalez/WENN.com)

“Mr Schmitz and Mr Hans Krug. I would be ashamed to even treat an animal in this way, as you tried to subdue me yesterday … Even if I worked above and was very happy to receive the recognition of a lady from Aachen … who made me a present of three tomatoes ... I have already heard how Mr Krug told her: ‘You can eat everything but E. K. is not to have anything to eat’ ... I am imprisoned in my cell without a bucket and with only one blanket.”

Already, of course, we want to know what happened to the two Gestapo men. Schmitz, it turned out, was caught after the war, briefly tried – and then freed. Krug disappeared in 1945. “The gentlemen know exactly how my situation is,” the prisoner wrote the year before. “Since three months I’ve been in the family way from a German officer. The Russian woman Maria next to me, who has three blankets and one bucket, was allowed to eat the tomatoes that had been given to me. These two gentlemen … [mis]treated by many other…a German woman, who carries a child beneath her heart. Ms. Else Kollmann. 29/9/44”

By that date, almost all the Jews in Cologne – their population in the Weimar Republic was around 16,000 – had been transported in cattle trains running to the Litzmannstadt ghetto in Lodz and to Riga, another directly to Sobibor. The documentation centre in the old Gestapo building – ironically the structure survived the war intact, its last hanging just a day before the first US troops entered Cologne – contains thousands of documents on the fate of the city’s Jews, even a postcard thrown out of a transport in March 1943 by 24-year old Helmut Goldschmidt. Incredibly, he survived Buchenwald and was freed in April 1945.

The archives at 23-25 Appellhofplatz also contain concentration camp documents: Karola Wolf, for example, work number 37725 marked “TRANSPORT 10/3/44”. Attached to it is a photograph of a young woman with short, neatly combed hair wearing a dark blouse with buttons at the front. Her mouth is set, slightly smiling, perhaps grimacing at the flashlight of the camera. She died in Belsen in May 1945.

The conditions in the Gestapo building have made visitors make comparisons with immigration centres in the US (Alamy/Oscar Gonzalez/WENN.com)

There is another document, a snapshot this time, of a woman and two children walking past snow-covered buildings in Lodz. In the foreground is a scaffold with a man’s body hanging from it, head shaven, it would appear – the picture was obviously taken secretly – and hands tied behind his back. The date is 21 February 1942. “The executed man,” says the caption, “is Max Hertz from Cologne.”

Thank God, you keep saying to yourself as you move through the old Gestapo building, that Germans today keep these essential historical memories alive in the most physical, tactile way. An official tells me the documentation centre and museum received 80,000 visitors last year, mostly foreigners but many of them German schoolchildren. Good, I say to him. They are the people who should come here. The people of Cologne are not spared. There are photographs of their corpses, piled high after RAF bombings – especially the first thousand-bomber raid on the city.

But there are also pictures sent home to their families by soldiers from Cologne who served in the Wehrmacht on the eastern front. They are of Russian partisans hanging from gallows, of Jews lying murdered in the streets of Polish and Russian towns. These were not sent home as proof of atrocities. They were souvenirs from sons and fathers and lovers at the front, horror postcards sent through the mail as others might have sent holiday pictures of crowded beaches or snow-covered mountains.

Nazi Nuremberg rallies Show all 4 1 /4 Nazi Nuremberg rallies Nazi Nuremberg rallies The Zeppelin grandstand (Zeppelintribune) can be seen at the former German Nazi party rally grounds on January 23, 2010 AFP/Getty Images Nazi Nuremberg rallies circa 1935: A rally, at the Zeppelin Stadium in Nuremberg, of German women serving in the Nazi Women's Labour Service Getty Images Nazi Nuremberg rallies 12th September 1938: German Chancellor and leader of the Nazi Party Adolf Hitler (1889 - 1945) addressing troops on the Zeppelin Field on the last day of the Nuremberg Congress Getty Images Nazi Nuremberg rallies 1933: National Socialist German Workers (Nazi) party rally at Nuremberg Getty Images

So how could those two Americans have visited this place – there are eyewitness descriptions obtained after the war of ferocious beatings administered in the Cologne cells – and thought of Palestine and Trump’s disgusting treatment of refugees on the Mexican border? Was this not, at the least, lacking in respect for the victims of infinitely more terrible acts of inhumanity?

I was going to conclude that this was true. There is proof enough of Israeli torture of imprisoned Palestinians, of mass Israeli killing on the Gaza border – but not on this scale. Gaza is a Palestinian Arab ghetto but there are no gas chambers awaiting its imprisoned people. No-one is being hanged or shot down by firing squads in the Israeli-occupied West Bank. And then I am struck by an article in the Israeli newspaper Haaretz by my old journalist friend Gideon Levy.

He was commenting on the German parliament’s vote two months ago to condemn the Palestinian boycott movement of Israel as antisemitic, accusing it of using “patterns and methods” used by the Nazis during the Holocaust. The Boycott, Divestment and Sanctions (BDS) movement, which is also supported by liberal Jews – especially in America – urges its supporters to maintain academic, business and cultural boycotts of Israel in an attempt to force its army’s withdrawal from the occupied West Bank, and to remove the vast wall that Israel has built, much of it on Arab land, between Israel and the occupied territory.

But Israel – and now the German parliament – have claimed that the boycott is Nazi-like in its methods. “‘Don’t buy’ stickers of the BDS movement on Israeli products,” the non-binding German resolution stated, “remind one [sic] of inevitable associations with the Nazi call ‘Don’t buy from the Jews’, and other corresponding graffiti on facades and shop windows.” And so even though the BDS movement is concerned with Palestinian rights and Israel’s failures in international law, its supporters are to be condemned as akin to Nazis.

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So now who is associating the Palestinian tragedy and Israeli occupation with the Nazis? German legislators are doing this. In Gideon Levy’s words in his Israeli newspaper column, “a non-violent struggle against war crimes will be declared illegal” if the German government adopts what he calls “this delusional resolution”. Levy writes of “the emotional blackmailing of Germany”, calls it “a march of folly” and scorns the Israeli authorities for adopting these tactics. “Fighting antisemitism,” he wrote, “solves any problems associated with explaining Israel’s actions. Just say ‘antisemitism’ and the world is paralysed. One can kill children in Gaza, then say ‘antisemitism!’ and squelch any criticism.”

And here lies a problem which the museum and archives of the old Gestapo building in Cologne cannot resolve. There are real antisemites in this world of ours. There are real racists, Trump is one of them. And Israel does itself no favours by falsely accusing honourable and decent men and women of being Nazis. We should all be fighting real antisemitism not “kotowing” (Levy’s word) to Israeli propaganda.

Yet now Trump himself joins in. He accuses four American congresswomen of using antisemitic language and of opposing Israel – thus conflating racism with anyone who objects to the Israeli government’s disgraceful policies towards the Palestinians. By the same token, it buys into the supposed relationship between the Nazis and anyone who demands justice for the poor, the occupied, the huddled masses yearning to breathe free.

We must draw our conclusions. The truth is that a boycott of Jews in Cologne preceded the deportation of Jews; the Nazis believed that their Jews were not German – just as Trump clearly believes that the four congresswomen are not American.

So can I really object this week to the words in the visitors book at the old Gestapo torture centre? If the Israelis make the connection to the Nazis, why can’t the two Americans who wrote those words in Cologne make a connection to Palestine? If Trump can urge a section of his own American people to leave their country – which was Hitler’s policy towards the Jews even before his genocidal intentions were clear to the rest of the world – then how can we escape the actions of Messers Schmitz and Krug? After all, they got away with it.

There are some valiant female voices memorialised on those cell walls. Who, for example, cannot warm to the soul who wrote this: “Girls, don’t subject yourselves to these sons of bitches! Be courageous and brave, even if you are facing a severe punishment.” Yes, of course, the circumstances were different. But when I came to the following cry from a French woman – it appears to have been written in pencil – how could I not think of the separation of children from their families in another country today?

“If there is a Frenchwoman, one day whose child is taken from her, against her will at the age of 11 days, you will understand what separation means and if I’m still alive that is only for my child, without her I would have long since left this world ... the guard … tells me I am sick, well, if one of you passes through here, she will understand the pain of a mother who has been separated from her child … She’s three weeks old today.”