David Kostinboi was born in 1926 in the village of Kornytsia, Ukraine, close to the Soviet-Polish border. His original last named was Kostinboim. When he was five years old, his family moved to the shtetl of Kunev, located on the border. When the Soviet-German war began in June 1941, the family did not want to leave. David's parents did not believe the rumors about what the Germans were doing to the Jews. However, when the enemy approached Kunev, David's mother had a bad premonition so she put some food to a sack and gave it to David saying, "Run away!" David fled from the doomed town with the retreating Red Army and then, at the age of 15, he experienced the humiliation and dangers of the Red Army's retreat of 1941.
By a miracle, David succeeded in escaping from the advancing Wehrmacht and reaching a village in the Urals far from the frontline. There he worked in a kolkhoz, and learned to perform all kinds of peasants work. A year later, when he was only 16, David was summoned to a recruitment office and "advised" to volunteer for the frontlines. He recalled: "I was never super-patriotic, and I did not join [the Red Army] in order to fight for the Soviet regime. I was going to fight against fascism. And, of course, I wanted to take revenge for my family. I assumed that it was most likely that the Germans had already killed all my relatives. And that was indeed the case. However, it was not the Germans who shot the Jews, but residents of our town ... It was Ukrainian policemen, former neighbors of the doomed, who did that." It was at the recruitment office that a clerk changed David's Jewish-sounding last name Kostinboim to the more neutral Kostinboi ("–boim?! And if, God forbid, you are captured as a POW?"). The official also recommended that David change the nationality in his documents from Jewish to Ukrainian but David refused.
David's training lasted for half a year. In October 1943 Private Kostinboi was assigned to be a machine-gunner in an infantry regiment deployed in eastern Belorussia. He recalled that being a machine-gunner was the most dangerous assignment in the infantry since in every battle the enemy first tries to kill the machine-gunners or at least put them out of action. War revealed itself to David Kostinboi as a phenomenon in which every day people were killed in the hundreds and thousands, commanders did not spare soldiers, and therefeore value of human life was nil. Kostinboi fought in Belorussia, then in Lithuania and, later, in Eastern Prussia. He was wounded several times, in the eyes. As a result he was blind until doctors succeeded in partially restoring sight to him. He finished the war being able to see with only one of his eyes.
The episode with the clerk at the recruitment office in the Urals to some extent was repeated at the front. On one occasion, his battalion commander sent several volunteers, including Kostinboi, to the enemy rear, to capture someone to provide information. The commander ordered the volunteers to hand over all their documents to his orderly. David did not want to do so. The commander retorted: "You should be the first to leave his documents since you are going to penetrate behind the German lines." David replied: "If I am taken prisoner, as soon as the Germans selected their Jewish prisoners to execute them, I will step forward and accept with pride being killed for my people." The commander shook his head, remarking: "What a fool you are!"
Kostinboi met VE-Day in Eastern Prussia. He recalled that the following day, May 9, he awoke, with a heavy hangover after the VE-Day celebration, on a military train. Finally, he realized that he was being sent to the Far East, to fight against Japan. Kostinboi was released from the army in December 1945.
Only one of his sisters succeeded in escaping from Ukraine and surviving.
After the war, Kostinboi worked as a teacher at a village school in western Ukraine.
 From the interview taken from D. Kostinboi in 2006, see https://iremember.ru/memoirs/pulemetchiki/kostinboy-david-semenovich/