Just found out about this, but a new (as in 65-year-old) Chagall crucifixion has returned to the art world:

[W]hen David Glasser, one of the museum’s chairmen, was perusing a Paris auction catalog a few months ago, he found it hard to believe what he saw: a previously unknown 1945 gouache by Marc Chagall. It was one of a small group of images Chagall made in direct response to the Holocaust, after he and his wife had fled France in 1941, after the German occupation and after he had begun to learn the details of the Nazi atrocities.
The gouache on heavy paper, which Chagall signed and titled himself lightly with a pencil in Russian — “Apocalypse in Lilac, Capriccio” — employs one of his familiar motifs, an image of a crucified Jesus, which he used as a metaphor for persecuted Jewry. But this crucifixion, painted in New York, where Chagall settled for several years, is one of the most brutal and disturbing ever created by an artist primarily known for his brightly colored folkloric visions.
“Apocalypse” shows a naked Christ screaming at a Nazi storm trooper below the cross, who has a backwards swastika on his arm, a Hitler-like mustache and a serpentine tail. Another small figure can be seen crucified and a second being hanged, and a man appears to be poised to stab a child. A damaged, upside-down clock falls from the sky. The darkness and directness of the work may have been a response not only to the war but also to the death of Chagall’s wife, Bella, a year earlier from a viral infection that might have been treated if not for wartime medicine shortages.
As the article mentions, Chagall adopted the theme of the crucifixion (lower case) as central to his work.
Perhaps most famously (and certainly more recognizably Chagall) in “White Crucifixion”:

The White Crucifixion is enigmatic. To describe it, the roughly square painting depicts a slightly distorted crucified Christ clad, not in the traditional loin cloth, but a Jewish prayer shawl; the cross bathed in a blistering white beam of light from above while all around are elements of the Jewish unrest and persecution taking place in Germany and Russia at the time. A synagogue burns, homes are destroyed, the Red Army marches, no match for the impending holocaust. The white and grey tones of the overall painting make all the more disturbing the bursts of colour as refugees flee aboard a boat or on foot, attempting to rescue sacred scrolls, or merely themselves, from the onslaught of terror. This was Marc Chagall’s Guernica.
The crucifixion is the perfect symbol for European Jewry, reflecting bigotry and persecution, not to mention the fact that Jesus was born, lived, and even died a Jew.
Chagall went to that particular well often:



Even at the tender age of 25, under full Cubist influence:

But the recently rediscovered crucifixion differs from the others in some key respects. While the characters on the periphery are Chagallian, and the ladder and clock are familiar from previous depictions, the central crime is the Holocaust, the German extermination of the Jewish people, not Russian pogroms. No flying fish or floating cows, no rich colors, no scenes of shtetl life.
One of the commentaries above calls the White Crucufixion “Chagall’s Guernica”, which has a point (not least because it was painted shortly afterwards).
But Apocalypse is also inspired by Picasso’s masterpiece (one of many):


I don’t think I need to spell it out.
There are different ways to engage with great themes (evil, in this case). One can study history (Hilberg’s Destruction of European Jews), read first-person accounts (Elie Wiesel, Primo Levi), watch documentaries (Night and Fog, Shoah, Sorrow & Pity).
I think art can makes its case, too. It slips past our intellectual defenses and stabs us right through the heart. God damn it.