In the aughts, once the US torture programs started getting public attention around 2003, I did my obsessive thing on the German Reich and the Holocaust.

During Operation Barbarossa, the SS was experimenting with eradication methods. The most common was the pogrom, endorsing the locals to massacre the undesirables. When they weren't undesirable enough or it was the whole village, the einsatzgruppen (death squads) had to come do it, usually forcing them to dig a mass grave and then executing them along the side.

It was messy and brutal and gross, and there was high turnover among the death squads (the US has a similar problem with its combat drone operators). And this was a major problem.

The SS experimented with other ideas, including deathwagons that would pipe the vehicle's exhaust into an enclosed chamber to kill dozens at a time, but even that was too harsh and too slow.

This is how the prototype genocide machine was made at Auschwitz. The program was contrived so no one who interacted with the live prisoners also interacted with the dead corpses. The guy who pushed the execute button was two persons removed in the chain of command from the guy who signed off on the execution order, and none of those people had to face the prisoners or the outcome. The point specifically was to make the process of massacre less stressful for the people involved.