HIROSHIMA, Japan — After his speech in Hiroshima on Friday, President Obama exchanged an emotional embrace with a bomb survivor who spent decades researching the American prisoners of war who were killed when the city was bombed.

Shigeaki Mori was 8 when the United States dropped the atomic bomb on Aug. 6, 1945.

I interviewed Mr. Mori, now 79, this week at his home in Hiroshima. He told me how he was walking to school when the bomb exploded, knocking him off a bridge and into a small, shallow river. He was lucky: The river protected him from the firestorm that followed. He remembered searching for food and water in the ensuing days but finding piles of charred bodies instead.

“Their mouths were open, because people had tried to identify them by their tooth fillings,” he said.

When he grew up, Mr. Mori worked at a brokerage house and, later, at a piano manufacturer. “But I’d always wanted to be a historian,” he said.