On 14 September 1946, Ivan Serov, Deputy Commissar of the NKVD, reported to Joseph Stalin the results of the investigation into the death of Stalin’s son Yakov Dzhugashvili. 

Since 27 June 1941, Yakov Dzhugashvili had been in the army as a commander of the artillery with the rank of senior lieutenant. He vanished near the city of Liozna in Belarus on 16 July 1941. On 18 July 1941, according to German archival documents, Yakov Dzhugashvili was brought to the headquarters of Field Marshal General Günther von Kluge. He was then moved from one concentration camp to another for two years and in October 1942, he was transferred to Sachsenhausen - a concentration camp predominantly for political prisoners in Oranienberg, Germany.

The circumstances in which Yakov Dzhugashvili died were investigated by a special commission directed by Heinrich Himmler. On the evening of 14 April 1943, SS Rottenführer Konrad Hafrich witnessed that Yakov Dzhugashvili did not follow orders to enter the barracks and demanded a meeting with the camp commander; he then suddenly crossed a neutral zone and grabbed a high-voltage wire with both hands. Hafrich shot him in the head; Dzhugashvili’s body fell on the wire and was left hanging on it.

The captain of the guard, SS Unterscharführer Karl Jüngling, the last one to communicate with Dzhugashvili, claimed it was not an attempt to escape, but an “act of despair by a man who was ready for everything”.

There is a version that Stalin was offered his son in exchange for Field Marshal Friedrich Paulus, but Stalin allegedly replied “I won`t exchange a Field Marshal for a soldier”. However, there’s no documentary evidence of this.

In the book ‘Twenty letters to a friend’, Joseph Stalin’s daughter, Svetlana Alliluyeva, wrote: “In the winter of 1942/43, after Stalingrad, my father suddenly told me during one of our rare meetings: ‘The Germans offered to exchange Yasha for one of their own. Would I bargain with them? War is war!’” And likewise, in his memoirs, chief of staff and deputy supreme commander Marshal Georgy Zhukov recalled that during one of his walks with Stalin he told him: “Yakov won't get out of captivity. The Fascists will shoot him.”

Source: Yakov Sukhotin. The Son of Stalin. Life and death of Yakov Dzhugashvili. - L.: “Lenizdat”, 1990.