Wiernik grew up and lived with his family in
Kobryń, Poland (then part of the Russian Empire), where he followed his father in becoming a master cabinetmaker. To avoid competition with artisan family members (
Natan Wiernik) who were also master cabinetmakers, they moved to
Biała Podlaska. From 1904 Jankiel Wiernik was a member of the
Bund movement. He lived in Warsaw and worked as a property manager at a house owned by the family of
Stefan Krzywoszewski (1886-1950), a popular writer, publisher and theatre director
in the Interbellum. When World War II began with the 1939
invasion of Poland, Wiernik was 50 years old. In late 1940 the German Nazis created the
Warsaw Ghetto, and Wiernik was forced to relocate there along with all
Polish Jews in the capital. He was transported to Treblinka on 23 August 1942, during the murderous
Grossaktion Warsaw. Following his successful escape from the
extermination camp in August 1943, he was rescued by the Krzywoszewski family. He remembered the horrors of the enormous
pyres, where "10,000 to 12,000 corpses were cremated at one time." He wrote: "The bodies of women were used for kindling" while Germans "toasted the scene with brandy and with the choicest liqueurs, ate, caroused and had a great time warming themselves by the fire." Wiernik described small children waiting so long in the cold for their turn in the gas chambers that "their feet froze and stuck to the icy ground" and noted
one guard who would "frequently snatch a child from the woman's arms and either tear the child in half or grab it by the legs, smash its head against a wall and throw the body away." At other times "children were snatched from their mothers' arms and tossed into the flames alive." He was also encouraged by occasional scenes of brave resistance. In chapter 8, he describes seeing a naked woman escape the clutches of the guards and leap over a three-metre high
barbed wire fence unscathed. When accosted by a Ukrainian guard () on the other side, she wrestled his machine gun out of his grasp, killed the guard, and shot another guard before being killed herself. When the SS recognized that Wiernik was a professional carpenter, they put him to work constructing various camp structures, including additional gas chambers. Given his skills, Wiernik was not subjected to the same treatment as others and no longer had to handle dead bodies. He attributed his survival to being able to build structures needed in the camp. Given the shortage of skilled construction workers accustomed to the killing process, Wiernik moved between the two divisions of the camp frequently. As a result, he became an important contact between the camp zones when the revolt was being planned. ==Escape==