(CNN) - The old man exited a car and immediately ran through the forest to what he remembered was a mass gravesite. “The Germans were here,” he said. "The people were in a row, and they just shot them in the back, one by one.”

Mikhail K, a man well into his 80s, said he was just a boy when he witnessed Nazi German soldiers massacre villagers in southern Russia in the 1940s. In 2012,photographer Markel Redondo accompanied him to a site near the village of Ladozhskaya in the region of Krasnodar to document his memories surrounding the atrocity.

Mikhail stood silently for a moment, “remembering and looking at the place,” Redondo recalled. "You could see there was something going on in his head.”

Redondo met Mikhail and other witnesses as part of an initiative by the Paris-based group Yahad – In Unum. The project aims to locate and document World War II sites where Jews and other victims were executed by Nazis and their allies throughout Eastern Europe. Yahad – In Unum has chosen not to reveal the witnesses’ full names.

Redondo spoke with CNN ahead of Days of Remembrance, when Holocaust victims are honored during the week of April 27-May 4.