In a series of harrowing recollections, Ben Zion Blustein said he was among just a dozen Jews who survived from his home town's population of up to 5,000.
At one point he and his family hid for days in a cellar. He escaped and they took their lives rather than be captured and killed.
"At this time in my testimony, it is the most difficult time in my life," he told the Old Bailey. "I dream about these friends night after night and I think about the people almost every day ... This trial is about 50 years too late."
Mr Sawoniuk, 77, from south London, is alleged to have murdered up to 20 Jews while serving as a police officer in Nazi-occupied Belarus in the Second World War. He denies the charges.
Mr Blustein, 76, a childhood friend of Mr Sawoniuk, was living in Domachevo, Belarus, when the Nazis invaded in June 1941. Having forced the Jews into a ghetto he said the Nazis set about "liquidating" them.
On the morning of the Jewish festival of atonement - Yom Kippur - in 1942 the Nazis gathered the Jews in the street. Fearing the brutality that was to follow, Mr Blustein, his parents and brother and sister hid in a cellar only a few metres across.
There, they waited and listened. "We heard lots of shooting. We heard shouts and cries and we could understand what had happened to them [the other Jews]" he said. "No one returned."
Wiping away tears, Mr Blustein said his family was forced to consider its position. "I heard my mother saying, 'Throughout our lives we were religious people and kept the laws of the Ten Commandments - why do we deserve to end like this? Why is there no one who can help is. What is the crime we have committed. We only want to live normal lives and bring up children'."
His stepfather decided they should take their own lives, using hoarded medicines. "We took leave of one another. My father took morphine. We took the drugs," he said. Only his stepfather died while the others suffered "terrible burning" inside.
They had no water. At this point his mother decided they should cut their wrists. Mr Blustein said his brother, Shlomo, seven, was afraid of blood and had to be persuaded by his 10-year-old sister that they would go to a place where they could live "normally".
As he prepared to kill himself Mr Blustein's mother told him he alone should try to escape. "My mother said to me, 'Son, do as I order you to do'," he said. He was never to see his family again.
Mr Blustein hid in the attic from where he could see the Nazis and local police rounding up Jews and "shooting children". At one point he saw an 80-year-old Jew, Shaya Idel, dressed in a prayer shawl and carrying the Talmud, being bayoneted by police who then set fire to his beard. Asked if he recognised any of the police involved, Mr Blustein replied: "Andrusha [Mr Sawoniuk's nickname] was there."
"The shawl was already red with blood. The Ukrainian police went after him and stabbed him with bayonets.
"They set fire to his beard and his sidelocks. I did not hear one cry from this Jew. They dragged him and hit him and he disappeared from the horizon."
Eventually Mr Blustein was forced to work for the Nazis at their stables. There, after the murder of another Jew, Mir Barlas, he said he spoke to Mr Sawoniuk. "What I understood from what he told me ... that he killed him and Andrusha said to me that Barlas had been very courageous," he said.
Cross-examined by William Clegg QC, for the defence, Mr Blustein was asked if, 57 years on, his memory might be at fault. "Things I want to forget, I don't remember. Things that are important to me, I will never forget," he retorted.
"Such things a man can never forget and I thank God who gave me good memory that I can remember all these things and I come to this trial as a witness, as a mouth, for the tens and maybe the hundreds who were killed by this man, to be their voice.
"I do not seek revenge - I trust that the English legal system is fine enough to find the most suitable penalty."
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