Hours into “Shoah,” Claude Lanzmann’s colossal 1985 documentary about the Holocaust, an urbane, silver-haired man sits before the camera in suit and tie, gathering his courage to tell a story. This is Karski. He takes a breath.

“Now I go back 35 years,” he begins, a strong Polish accent flavoring his words. But almost instantly his poise crumbles, and he begins to weep; the memories he is being asked to tap are too excruciating.

“No. I don’t go back,” Karski says. As the camera watches, he flees the room.

To Strathairn, who saw the nine-hour-plus “Shoah” in a single stretch when it was first released, that “microscopic moment” in the movie is “the portal into 35 years of silence.” In the theater’s dressing room, glasses perched atop his head, he traced a timeline of Karski’s life on the tabletop — events that, in Strathairn’s mind, are all contained somehow in that brief, tormented bit of film.

At the start of the timeline, Karski’s childhood, when his Roman Catholic mother taught him to tell her when he saw “bad Catholic boys” throwing dead rats at Jews, so she could do something about it. Next his late 20s, in German-occupied Poland, when Jewish leaders sneaked him into the Warsaw Ghetto and a German concentration camp, so that he could tell the world what he’d seen happening there. Then the many postwar years when, having written a book about his experiences, he no longer spoke of them, even as he taught for decades in Georgetown University’s School of Foreign Service. Last, the chapter that began in the late 1970s, when Lanzmann convinced him that it was his responsibility to bear witness again for “Shoah” — which, after that initial loss of nerve, Karski did, and kept doing elsewhere.

“Remember This,” which opens on Thursday in Brooklyn and is scheduled to run through Oct. 9, was created as a multicharacter piece at Georgetown for a centennial celebration in 2014 of Karski’s birth. Written by Derek Goldman, the artistic director of the university’s Laboratory for Global Performance and Politics, and one of his former students, Clark Young, who graduated in 2009, it was initially titled “My Report to the World,” a phrase borrowed from the subtitle of Karski’s best-selling 1944 war memoir, “Story of a Secret State.”