It’s most likely that Menachem Bodner last saw his identical twin in 1945, in Dr. Josef Mengele’s gruesome Auschwitz laboratory. He was 4 then and doesn’t remember his time in the notorious death camp. But in the 68 years that have followed, Bodner says he’s “always” been certain he was one of a pair. He just didn’t have any proof until this past year. Now, he’s searching for Jeno, a man who probably looks just like him, and who has a distinctive “A-7734” tattoo on his forearm. And 1 million Facebook users are helping him look.

Mengele, known among prisoners as “the Angel of Death,” was deeply fascinated with twins and used them for research experiments in his macabre Auschwitz lab. Thankfully, Bodner, now 72, has no recollection of the cruelty he most certainly endured while undergoing experiments, though he can remember a sense of paralyzing fear. Unfortunately he also has few impressions of his family’s prewar life in a small town east of Munkacs, Hungary, which is now in the Ukraine. But despite the lack of memories from a war-marred childhood, Bodner says that throughout his life he’s felt a deep connection with his twin—and is positive he’s still alive and out there. But where?

Until last May, Bodner didn’t even know that his own name was once Elias Gottesmann. Now he knows that. And he knows for certain that he has a twin—thanks to the Nazis’ dogged, pathological documentation of their crimes. Ayana KimRon, a professional genealogist in Israel, found the evidence, clearly written in a record put together by the organization Candles, of twins who were “identified as having been liberated at Auschwitz or from a subcamp”: