Note: this post contains lots of images.
It is usually claimed that the scene depicts a gassing in Mogilev. However there were also some testimonies about similar early gassings elsewhere (Minsk), so we should make sure that we have the right location. In order to do this we should examine photos of the Mogilev psychiatric hospital, specifically of the location where the gassing is claimed to have taken place.
After some searching we were able to find a good photo of the place in Istoriya mogilyovskogo evrejstva. Dokumenty i lyudi, book 2, part 2 (2nd. edn.), 2010, s. 194.
The caption reads: "The modern view of the building of the psychiatric hospital in which the fascists carried out an action of extermination of the patients."
Based on several indications we decided that the window on the right is the most likely candidate for the exact location shown in the film. We then prepared two images for a comparison. One from the photo above:
And one from the film:
Note however that the photos were taken from different angles. Therefore we "unskewed" them with the Perspective Crop tool and then overlaid them on top of each other (which required some stretching). By controlling the opacity of one of the images we could then create a series of images where one photo "blends" into another, allowing for a direct visual comparison. We also marked several areas on the photos with the more obvious coincidences.
Here is an animated gif that we prepared based on these images.
We're satisfied that the photos depict one and the same wall. The areas marked on the images - the "straight line", the extruding lower part on one image (and the human shadow distorted by this part on the other image), the positions of the matching areas in relation to each other, as well as to the extruding part and to the "straight line", cannot be explained away as a coincidence due to the same brickwork pattern. Moreover, the parallel rows of bricks do not perfectly align with each other on the same photo - and the alignment "defects" are same in both images (cf. especially the large circle on the right).
Our conclusion is therefore that the footage was, indeed, shot at the Mogilev psychiatric hospital.