In 2008 revisionist Thomas Kues published a detailed comparison of various accounts given by Freiberg over the years, but the earliest one then known to Kues was Freiberg's testimony at the trial of Adolf Eichmann in June 1961; Kues' colleague Carlo Mattogno mentions a 1945 account given by Frieberg in their 2013 book (p. 1179).
The original 1946 edition of the The Black Book covers Sobibor with Ehrenburg's article "The Button Factory"—which had been published in the New York newspaper PM on September 11, 1944. In 1980 edition of the The Black Book, Ehrenburg's article is replaced by one titled "The Uprising at Sobibor", and the same article appears again in 2003 version The Complete Black Book of Russian Jewry.
Seemingly unknown in literature on Sobibor, is the article which is produced in facsimile below. It appeared in the Information Bulletin, on September 15, 1944, which was a publication of the Soviet embassy in Washington D.C., similar to Soviet War News, the daily publication of the London embassy.
Freiberg is quoted at length in the Bulletin article, and some of the quotes appear again in The Black Book (1980 and 2003), which also states that the quotes were taken from a written account Freiberg made of his experiences, dated August 10, 1944; Ehrenburg didn't mention Freiberg in his article that appeared in the original 1946 version.
Freiberg's detailing of the collapsible gas chamber floor—which was mandatory in post-war accounts of Sobibor—features in both the Bulletin article and The Black Book (1980 and 2003), but absent from the latter is the estimated death toll of 2,000,000 and the following quote from Freiberg about the collection of human fat for shipment to Germany where it was made into soap:
"At the end of 1942 the cremation of corpses began in the third camp. rails were laid and fires were constantly kept burning under them. ... Thousands were burned everyday; the fires were kept burning day and night, the flames rising very high. ... Special containers were fitted to the rails for collecting human fat. The furnaces were manned by a special crew of 150 prisoners. The ashes were collected in sacks and sent to Germany for use as fertilizer. The fat was packed in barrels, also for shipment to Germany. The Germans said that it made good soap."