A few months later his mother moved with her four children to her parents' house in Warsaw, which was situated in the ghetto that had been established in November 1940 in the heart of the Jewish Quarter.

A year later, in autumn 1941, when conditions in the ghetto had worsened and tens of thousands of its residents had died or were killed, this spurred him to escape from the ghetto with the assistance of a smuggler; Freiberg escaped to the remote town Turobin in the district of Lublin, where the Jews, including the family of his father, lived with a sense of relative calm.

In October 1943, Freiberg participated in the Sobibor prisoners' revolt and he managed to escape into nearby woods and joined the Joseph Serchuk's Jewish partisan unit in the Lublin area of occupied Poland until the Soviet Army liberated the region in July 1944.

Once in Germany he joined a training group consisting of Holocaust survivors, where he met his future wife – Sarah, a refugee from the Soviet Union.

Four years later, in 1965, he was invited to Germany to testify at the trial in Hagen, where SS officers were tried for acts committed in Sobibor.