WORLD WAR II KILLING OF SOVIET CIVILIANS ACCUSED OF BEING PARTISANS ON THE EASTERN FRONT BY A GERMAN FIRING SQUAD, SEPTEMBER 1941

 World War II killing of Soviet civilians accused of being partisans on the Eastern Front by a German firing squad, September 1941

There are two reasons for this; one, why not headshot, and two, why not just a shooter? Military firing squad. 

They do not shoot the head because, while effective at killing a person, shooting the head will usually destroy any identifiable facial features.

This is not desirable, as it means that you cannot have an open-casket funeral (if you are inclined to be magnanimous)

 or display your body as proof that you are, in fact, dead. They have a multiple shooter firing squad to give everyone diffusion of responsibility. 

Have you ever wondered why the Nazis went to the trouble of building camps and gas chambers instead of simply machine-gunning their victims? 

The Third Reich did some research into the "best" way to commit genocide and discovered that, even with all the conditioning to view Jews and undesirables as "subhuman," shooting unarmed people tended to take a toll on a soldier's mental health.

. Unless the man in the image above is a literal psychopath, he will have some level of mental stress as a result of what he is doing. 

And since psychopaths are about 1% of the population, it is not feasible to specifically recruit only psychopaths for firing squads (or, for that matter, extermination camps, gas chambers, etc.)

So, rather, each soldier is given a rifle with one round. A certain number of magazines have "blank" cartridges, which basically just make an explosion, and the others have "live" ammunition, which will kill the target. 

Therefore, each soldier in the firing squad can believe that he fired a blank cartridge and did not kill the prisoner. I hope this helps!