Cameron A. Munro has recently published "Engineered for Mass Murder – The Nazi Gas Vans: 1939–1945", a book in which he presents 15 photographs depicting a homicidal gas van built on a petrol-powered Diamond T chassis.
These photographs were taken in April 1942 by SS-Rottenführer August Vielkind of the Waffen-SS reserve, who was part of the advance detachment of Sonderkommando 7a of Einsatzgruppe B, marching from Klintsy via Gomel to Sychyovka. The images were used by prosecutors in Dortmund during investigations into members of Sonderkommando 7a. However, as Munro notes, it seems they "did not forward the photographs to West-German investigators of other units" and "the photographs then lay forgotten in the files of the Landesarchiv Nordrhein-Westfalen in Münster for many years".
It’s remarkable that such historically significant material can still be discovered after so many years. And fittingly - characteristic of authentic historical research - the deeper one digs, the more corroborating rather than contradicting evidence tends to emerge.
I highly recommend it to anyone interested in the history and mechanics of the Nazi homicidal gas vans.