A photograph freezes a moment in time. A young girl stares out from the door of a train, her head covered in a scarf, her expression a strange mixture of weariness and fear.

The girl's name? Anna Maria "Settela" Steinbach. Ten years old when the photo was taken. Three months later Settela was dead - gassed at Auschwitz concentration camp, along with her mother, brothers and sisters.

For decades Settela's face was an icon of children in the Holocaust. Her name unknown, she was simply called "the girl with the headdress". Along with Anne Frank, she was a haunting symbol of what had been done to Dutch Jewry.

But in 1994 a journalist, Aad Wagenaar, discovered her identity. Using the numbers that appeared on the train car, Wagenaar was able to determine the train's day of travel, May 19, 1944, and its passenger list.

Settela wasn't Jewish. She was Roma (alternately Romani, Sinti, Gypsy). It was assumed the girl was Jewish because even in the 1990s - a half-century after World War II - the genocide of the Roma people was hardly known to the world.

In America, The Diary of Anne Frank was required reading at my Florida public school, as was Eli Wiesel's Night. With Native American history absent from history classes, the death of six million European Jews was my first knowledge of genocide.

As I read about Wiesel's "faces of children … turned into wreaths of smoke beneath a silent blue sky", Jewish children were the face of the Holocaust for me. I didn't know that children such as Settela had existed.

Yet estimates by Roma historians state that as much as 70-80 percent of the total Roma population in Europe at the time were murdered in the Nazi madness.

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Despite this, recognition of the Roma Holocaust remains scant. Historians term it "under-studied", "neglected", "hidden".

"We have consistently been put into the 'others' category - along with Jehovah's Witnesses, homosexuals, Poles and Catholics, as if we weren't part of the Final Solution," says Ian Hancock, director of Romani Studies at the University of Texas, Austin.

Experimenting upon Roma children, Mengele placed them in pressure chambers, tested drugs on them, amputated body parts, attempted to change eye colour by injecting chemicals into children's eyes, and froze them. The rare child to survive these 'experiments' would be murdered and then dissected.

While Nazis murdered numerous groups for their beliefs or actions - trade unionists. pacifists, communists, Spanish Republican exiles and Jesuits, among others - they applied a consistent policy of extermination only against three groups: the handicapped, Jews, and Roma.

The campaign in Germany against the Roma began shortly after Hitler assumed power in January 1933. On the basis of discriminatory laws already in place, Roma were barred from marrying Germans, castrated and sterilised, and shipped to labour camps.

An office to combat what SS chief Heinrich Himmler called "the Gypsy nuisance" opened in Munich in 1936. And five months before Kristallnacht, Roma were rounded up in what was called "Gypsy Clean-Up Week".

Then in December 1938, the first known reference to "The Final Solution of the Gypsy Question" appeared in a document signed by Himmler.

In 1939, Dr Kurt Hanneman wrote in the Journal of the National Socialist Union of Doctors: "Rats, insects and fleas are part of nature, just like Gypsies and Jews … We must gradually eliminate these pests through biological means." That same year, 250 Roma children were murdered in Buchenwald - used as guinea pigs in a test of Zyklon-B gas crystals.

Warsaw Ghetto Remembrance Day, April 19, is commemorated annually to remember the many Jews who fought - and died. How many people know that Roma were also imprisoned inside?

Roma were trapped inside Lodz ghetto, too. Arie Princ and Mendel Grossman, photographers who were the first to enter, wrote: "We could not recover for a long time from the shock, reading the inscriptions in German left by the Gypsies on the walls."

And Roma were present in every concentration and extermination camp.

Josef Mengele was the most infamous of Germany's racial theorists. Witnesses say Roma children called him "Onkel Mengele" because he would bring them sweets and toys, personally escorting some to the gas chambers afterwards.

Experimenting upon Roma children, Mengele placed them in pressure chambers, tested drugs on them, amputated body parts, attempted to change eye colour by injecting chemicals into children's eyes, and froze them. The rare child to survive these "experiments" would be murdered and then dissected.

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The full extent of Mengele's experiments will never be known because most records were destroyed. Instead we have first-hand testimonies, such as this from Vera Alexander, a Jew who survived Auschwitz, where she had looked after 50 sets of Roma twins: "One pair of twins called Guido and Nina was barely older than four. Mengele picked them up and brought them back mutilated in a perverse way. They had been sewn together at the back like Siamese twins. Mengele had also connected their veins. Their wounds were suppurating, they cried day and night. Their mother, I remember that she was called Stella, had somehow been able to get hold of some morphine and used it to put an end to the suffering of her children."

Eli Wiesel, the world's most famous Holocaust survivor, late in life became a vocal advocate for victims of South African apartheid and Argentina's "disappeared". He recognised the suffering of Bosnians, Kurds, Armenians.

But in 1992, as a member of the advisory council of the US Holocaust Memorial Museum, he lobbied successfully against recognising "non-Jewish" victims in the museum's permanent exhibition.

There are "rules" about the Holocaust. In July 1998, Roberto Benigni premiered Life is Beautiful at the Jerusalem Film Festival. I remember how tense and restless the hall was throughout the screening. Who was this Italian to make a "comedy" about the Shoah?

The most important rule has been Wiesel's dictum: "The Holocaust was a unique and uniquely Jewish event."

Addressing 600 Jewish leaders at the World Jewish Conference by video conference on April 23, two days before visiting the Holocaust Museum in Washington, US President Donald Trump - in stark contrast to his earlier statements - followed those rules carefully.

"Six million Jews, two-thirds of the Jews in Europe, murdered by the Nazi genocide … We mourn, we remember, we pray, and we pledge never again, I say it, never again."

It's hard to imagine Trump praying. It's even harder to imagine him genuinely moved by the Nazi Holocaust (or by any other genocide). And Trump's repeated "never again" feels tired, devoid of meaning.

In contrast, on the same day as Trump's speech, a thirtysomething Jewish-Israeli posted this on Facebook: "It's Holocaust Memorial Day in Israel. Between Syria, the refugee crisis and Chechnya LGBT death camps, I can no longer say 'never again' with a straight face."

A generational change is under way. Six million Jews did die in the Holocaust; antisemitism and Holocaust denial are real. And, simultaneously, the Holocaust narrative focusing on the exclusivity of the Jewish experience is wrong - and must change.

Gina Benevento is a former UN diplomat based in Jerusalem, now living and working in Madrid as a strategic communications consultant.

The views expressed in this article are the author's own and do not necessarily reflect Al Jazeera's editorial policy.