So that we might learn conclusively and in detail about the fate of the human transports leaving the ghetto, Zalmen Frydrych (Zygmunt) was ordered to follow one of the transports to the "Aryan side". His journey "to the East", however, was a short one, for it took only three days. Immediately after leaving the ghetto walls he established contact with an employee of the Warsaw Danzig [Gdanski] Terminal working on the Warsaw--Malkinia line. They travelled together in the transport's wake to Sokolow where, Zygmunt was told by local railroad men, the tracks forked out, one branch leading to Treblinka. It proved that every day a freight train carrying people from Warsaw travelled in that direction and invariably returned empty. No transports of food were ever seen on this line. Civilians were forbidden to approach the Treblinka railroad station.
This in itself was conclusive proof that the people brought to Treblinka were being exterminated somewhere in the vicinity. In addition, Zygmunt met two fugitives from the death camp the following morning. They were two Jews, completely stripped of their clothes, and Zygmunt met them on the Sokolow market place and obtained the full details of the horrible procedure. Thus it was not any longer a question of rumours, but of facts established by eyewitness accounts (one of the fugitives was our comrade Wallach).
After Zygmunt's return we published the second issue of On Guard with a detailed description of Treblinka. But even now the population stubbornly refused to believe the truth. They simply closed their eyes to the unpleasant facts and fought against them with all the means at their disposal.
The publication to which Edelman refers is, I believe, the issue of Oyf der Wach [this name has various spellings] dated September 20th, 1942. Jansson discusses the Oyf der Wach issue in this blog piece but downplays it as being far more minor than the report of November 15, 1942, which contains the "steam room" description. Whilst it is less detailed than the later report, it was certainly not a minor piece, as shown by Edelman's recall so many decades later. Furthermore, Jansson omits the fact that the Oyf der Wach article mentions gassing and electricity, but not steam, as Jansson would have seen on page 245 of Arad:
The bath was actually a house of murder. The floor in this barrack opened up and the people fell into a machine. According to the opinion of some of those who escaped, the people in the barrack were gassed. According to another opinion, they were killed by electrical current.
The German text of the same document is printed from page 443 here.
It is known that Zalmen Frydrych (Zygmunt) returned to Warsaw "on the sixth day of the deportation" [Report from the Jewish Workers Underground Movement · 22 June 1943], which would be 27.7.42, two months before Rabinowicz is quoted by Lewin as mentioning "steam". This would seem to refute any notion (which Jansson appears to imply) that steam preceded or exceeded gassing as the method claimed in the sources.
Jansson is also apparently unaware that Oyf der Wach was published by the Bund, whereas the Rabinowicz testimony and the November 15th report were produced by Oneg Shabbat.
Most importantly of all, Jansson omits the fact that Nick Terry quoted the Oyf der Wach extract, including the reference to gassing on pages 60-61 of the Critique. Moreover, Jansson ignores how the four preceding pages of Nick's chapter included an account of how the Armia Krajowa had heard about gassing in August. Jansson has thus:
a) Mischaracterized the Oyf der Wach article, omitting its discussion of gassing
b) Omitted the discussion of that article in the Critique
c) Overlooked the significance of the Oyf der Wach article in the timeline concerning the Warsaw ghetto's publication of Treblinka accounts.
d) Overlooked the accounts of gassing that had already been disseminated in August 1942.
Update 10.6.2015 Jansson's latest effort shows his failure to grasp logic:
Within a few days of the onset of deportations from Warsaw there were reports that the resettlers were going to their death. What killing method would be claimed took some time to determine.
Jansson fails to explain why this should be unusual. It was easy to determine that Jews were being killed, from the fact that masses of Jews were entering the camp daily but never leaving, and that some of the escapees were gravediggers. It was far harder to determine how they were being killed, because nobody was being given a grand tour of the killing facilities.
Jansson is also still blissfully unaware that two organizations were involved in gathering the information, the Bund and OS, and their sources were different. Of course the sources were imperfect, because nobody had direct access to a gassing engine and there were three different ways to infer what could be seen or heard indirectly. Thus we get gas, electricity and steam. No sane person should be surprised that such a range would exist in 1942-43, or that it would take time for the real method to emerge. This is indeed acknowledged by Ringelblum, whose final entries focus on the range of information coming in - "gas, steam, electricity." Only deniers would find that odd in 1942-43.