Dietrich Bonhoeffer was a prisoner at the Nazi Concentration camp at Buchenwald.

After a time further prisoners arrived at Buchenwald, including English officers, Hugh Falconer and Sigismund Payne Best, Best had been lured by an SS commando into an ambush in the Dutch border town of Venlo in 1939 and taken into the Sachsenhausen concentration camp. His book The Venlo Incidentwritten soon after the war, is the only reliable source we have for the last weeks of Dietrich Bonhoeffer’s life. All other testimonies were written a long time after the war.     

(Ferdinand SchlingensiepenDietrich Bonhoeffer 1906-1945: Martyr, Thinker, Man of Resistance, 369).