Prime Minister Justin Trudeau paid an emotional visit on Sunday to Auschwitz-Birkenau, the site of the former Nazi death camp, in southwestern Poland.

He was given a personal glimpse into one of the darkest chapters in human history through the recollections of a Holocaust survivor and his family. As they walked the dusty lanes of the former concentration portion of the camp, which is now a museum, Nate Leipciger recalled how some of his Nazi guards were brutal, yet occasionally capable of inexplicable acts of kindness.

Trudeau touches a rail car during a tour of the site in Poland. (Adrian Wyld/Canadian Press)

It was a raw memory, impressions witnessed through the eyes of a young boy, but recounted by an old man. Leipciger was born in Chorzow, Poland, and was sent to Auschwitz as a teenager. He had been in the line for the gas chamber, but survived because his father negotiated with an SS guard to get him into the slave labour pool.

After the war, Leipciger immigrated to Canada, where he obtained an engineering degree and became a leader in the Jewish community in Toronto.

Locks of human hair

The hardest part for him, he told Trudeau, was looking at the display of hair shaved from the heads of victims, which is sealed behind a glass wall. He says he often wondered, in previous visits, whether there are locks belonging to his mother and sister among the carefully preserved piles.

Trudeau was deeply affected by what he saw and wiped away tears several times as he and Liepciger surveyed the massive ruins and shattered masonry that had once been gas chambers where millions met their deaths.

Trudeau made a point of asking to visit Auschwitz following the NATO summit in Warsaw.

Justin Trudeau listens to Nate Leipciger, second from left, during the tour, with Dr. Piotr Cywinski, left, and Rabbi Adam Scheier and Foreign Affairs Minister Stéphane Dion, right, in Auschwitz, Poland. (Adrian Wyld/Canadian Press)

When he wrote in the book of remembrance, his reflection seemed to speak as much to today as the horrors of the past.

"Tolerance is never sufficient," Trudeau wrote, "Humanity must learn to love our differences."

Trudeau writes of 'capacity for evil'

He had to switch pens, at one point as he scratched out a longer message. The first one ran out ink.

Trudeau went on to write: "Today we bear witness to humanity's capacity for deliberate cruelty and evil. May we ever remember this painful truth about ourselves and may it strengthen our commitment to never again to allow such darkness to prevail. We shall never forget."

Some of Trudeau's critics, who struggled to get the Liberal government to recognize the slaughter of religious minorities in Iraq as genocide, may take note of the inscription.

The Prime Minister of Canada Justin Trudeau <a href="https://twitter.com/JustinTrudeau">@JustinTrudeau</a> visited the <a href="https://twitter.com/AuschwitzMuseum">@AuschwitzMuseum</a>. [Auschwitz II-Birkenau] <a href="https://t.co/eAIsSNVkqc">pic.twitter.com/eAIsSNVkqc</a> —@AuschwitzMuseum

Foreign Affairs Minister Stéphane Dion did declare, in mid-June, that the atrocities committed by the Islamic State in Iraq and Syria against the minority Yazidi people constituted genocide.

But the declaration only came after a United Nations statement, something critics said the government shouldn't have waited to hear.

Liepciger says he believes the message he was trying to convey to Trudeau got through and he knows the two of them cried together.

It was a lesson for Trudeau, the new statesman, on the world stage.

"You must realize the dangers and you must confront them. You cannot ignore or write them off. You must face reality in the world we live today," he said.

Canadian tourists at Auschwitz

The discreet visit took place amid groups of tourists, including Canadians, some of whom stopped when they recognized Trudeau.

How the horrors of the past can be repeated today was on the mind of a Toronto high school teacher, who watched the prime minister walk past.

"Unfortunately look at what's going on another places in the world," said Mel Stein, a high school teacher from Toronto whose father also survived the death camp. "It's impressive that he came, but if any citizen of Canada should see this, it's him."

Trudeau was following in the footsteps of Jean Chrétien and Stephen Harper, who also visited Auschwitz during their terms as prime minister.