Around this time of the summer in 1944, two runaway Jews arrived at a monastery near the Slovak capital, Bratislava, hoping to meet a Vatican diplomat.

The two, Czeslaw Mordowicz and Rudolf Vrba, had escaped separately from Auschwitz weeks earlier and they wanted to alert the world that the Nazis were in the midst of massive killings at what was then a little-known camp in occupied Poland.

Both men survived the war, even though Mr. Mordowicz was recaptured and sent back to Auschwitz. They both later became Canadian citizens.

Mr. Vrba, who wrote a book and appeared in the landmark documentary Shoah, passed away in 2006, his death reported in the world’s major newspapers.

Mr. Mordowicz died of a stroke in Toronto on Oct. 28, 2001. His death drew no public notice despite his role in alerting the world to the genocide perpetrated by the Nazis.

While he did talk to historians and gave video testimonies for the U.S. Holocaust Memorial Museum and the USC Shoah Foundation, he was not a household name.

His daughter, Dagmar Wertheim, said her father shunned publicity and his remarkable life was known by few people aside from Holocaust scholars.

In May, 1944, Mr. Mordowicz and another inmate, Arnost Rosin, managed to break out of the Auschwitz-Birkenau complex, making their way to Slovakia.

Mr. Vrba and another inmate, Alfred Wetzler, had escaped the previous month and were also in Slovakia with similar aims. Together with information from another escapee, Jerzy Tabeau, their detailed, eyewitness accounts were assembled into a document that came to be known as the Auschwitz Protocols.

While earlier escapees had disclosed the existence of the camps, the Protocols made the biggest impact. The document was smuggled out to Switzerland and the Vatican. It was disseminated by the U.S. government and both the BBC and The New York Times reported its contents.

The information from Mr. Mordowicz and Mr. Rosin, which also formed part of the Protocols, was particularly significant because it provided the first account of the most murderous chapter in Auschwitz history, the deportation and killing of the Hungarian Jews.

“Wetzler and I saw the preparation for the slaughter. Mordowicz and Rosin saw the slaughter itself,” Mr. Vrba wrote in the magazine Jewish Currents in 1966.

About 430,000 Hungarian Jews were eventually deported to death camps. The eminent Holocaust historian Martin Gilbert credited the Protocols with generating public pressure, however, that led the Hungarian government to halt the deportations in July, 1944.

“At last the reality of Auschwitz-Birkenau was clear to the outside world … the camp … was revealed to be the largest single killing centre in Europe,” Mr. Gilbert wrote in his 1981 book Auschwitz and The Allies.

The Protocols were entered as exhibits at the trial of top Nazi officials in Nuremberg and the trial of Adolf Eichmann in Israel.

“My father’s life reads like a history book,” Ms. Wertheim said in his eulogy.

Czeslaw Mordowicz was born on Aug. 2, 1919, in Mlawa, a town in central Poland. He was the eldest of the two children of Herman Mordowicz, a grain merchant, and his wife, the former Anna Wicinska, an actress in the local Jewish theatre.

Mr. Mordowicz was 20 and hoping to study engineering when Germany invaded Poland.

The family fled to Warsaw, then to another town, Plonsk. His parents and his sister, Rachela, later returned home to Mlawa, while he stayed with friends in Plonsk, helping them restore their grocery store, which had been looted by Germans.

He married his hosts’ 19-year-old daughter, Szulamit, and remained in Plonsk when the Jewish population was forced into a ghetto.

He worked under a German supervisor as a truck driver. One night, the German boss warned Mr. Mordowicz that the ghetto would be liquidated in the morning, and offered to smuggle him out.

He refused to abandon his wife and in-laws. Hours later, the SS deported everyone to Auschwitz-Birkenau.

Mr. Mordowicz was separated from Szulamit and her parents. “From that moment, I never saw them again,” he recalled in a video testimony.

He barely survived his first days as a slave labourer, loading bricks and gravel onto wheelbarrows. Then he got lucky. Since he could write in German, he became the clerk in his barrack.

He heard that his father was also in the camp. They had a short, tearful reunion through a camp fence, where he learned that his mother and sister had been sent to the gas chambers. A few days later, Mr. Mordowicz looked for his father and learned that he had died.

He kept thinking about escaping even though those who were recaptured were executed, their bodies propped up at the entrance gate with a sign saying: “Here I am again.”

In April, 1944, Mr. Vrba and Mr. Wetzler, two Slovak Jews who were also clerks, escaped. Concealing themselves under a pile of lumber at a remote end of the camp, they sprinkled tobacco soaked in gasoline to thwart the search dogs. After waiting three days for the manhunt to be called off, they left their hideout and slipped away.

In retaliation, all the Jewish barrack clerks, including Mr. Mordowicz, were flogged with 25 lashes and demoted to labour units.

Working in a gravel pit, however, gave Mr. Mordowicz the chance to escape.

He and other prisoners made a small dugout on a side of the pit, hiding it with planks and grass. On May 27, Mr. Mordowicz and Mr. Rosin crawled into the hideout, bringing with them two pairs of overalls, bread and water. They poured turpentine around to keep the dogs away.

After a few hours, sirens wailed when their absence was noticed at roll call. They heard the voices and barking dogs of search parties. At one point, the dogs pawed right above them, “as if in our heads,” but the men were not discovered.

Eventually, running out of air, they dug themselves out during the night and crawled past the watchtowers. Mr. Mordowicz said it was very dark but for the flames from the crematorium chimneys.

They swam across the Sola river, losing a pair of boots in the water. They each wore one of the remaining boots, wrapping the other foot with strips torn from their shirts. Later, they traded a wristwatch with a boatman for his footwear.

Cadging food from peasants, they moved in the forests at night. Near a bridge at daybreak, they saw German soldiers approach. Since they were in overalls, they pretended to be workers, staring and pointing at utility poles.

They headed east for Krakow but a farm woman warned that the Germans were rounding up civilians there to dig anti-tank trenches. So they turned south toward Mr. Rosin’s native Slovakia.

One day, they saw a matchbox on the ground with Slovak writing. They were now in Slovakia, which had a pro-Nazi government but where the deportation of Jews had been suspended.

They were arrested, but Mr. Rosin managed to alert an acquaintance, who told them to claim they were currency smugglers. The local Jewish community then paid their fines and they were released.

They met up with Mr. Vrba and Mr. Wetzler, who had arrived in Slovakia two months earlier. The four were questioned separately by Jewish leaders, who saw that their accounts checked against each other. They also met with a papal representative at a monastery near Bratislava.

The information from Mr. Vrba and Mr. Wetzler had been compiled into a 33-page report. Mr. Mordowicz and Mr. Rosin contributed a complement of seven pages.

The Mordowicz-Rosin report said that transports from Hungary started to arrive in mid-May, bringing 14,000 to 15,000 people daily, most of whom were immediately killed.

“Never had so many Jews been gassed since the establishment of Birkenau,” their report said, explaining that the crematoria worked day and night and large pits had been dug to burn more bodies.

“The exterminating capacity became almost unlimited,” their report said.

The four were still in hiding, so their names were withheld when the Protocols were circulated outside German-occupied Europe.

In the fall, Mr. Mordowicz was arrested by pro-Nazi militiamen, who accused him of being a Soviet spy and handed him to the Germans.

He claimed to be a runaway Jew and luckily they didn’t notice the prisoner’s number tattooed on his forearm, which he had covered with surgical tape.

He was deported back to Auschwitz. On the train, he chewed at his forearm until the tattoo was obscured by a wound. “I had nothing at my disposal, only my own teeth,” he recalled.

He also tried to warn the others on the train, but they were incredulous and beat him instead.

In Auschwitz, he considered killing himself, but long-time prisoners recognized him. They helped conceal his identity. Lale Sokolov, the camp tattooist, inked a flower pattern on Mr. Mordowicz’s arm to cover his old prisoner’s number. Mr. Mordowicz was later sent to a labour camp in Silesia, where he worked until it was liberated by the Red Army.

After the war, he returned to Bratislava, married another Holocaust survivor and worked as a factory manager. He immigrated to Israel in 1965, then, following retirement, moved to Toronto in 1985.

Mr. Mordowicz leaves his daughter, Ms. Wertheim, and a granddaughter, Shelly. He is predeceased by his first wife, Szulamit, who was killed in 1942 in Auschwitz, and his second wife, Ester, who died in Toronto in 1993.