Soviet troops retreating were machine gunned down by NKVD squads.
The opening scene of "Enemy at the Gates" showed that NKVD practice.
They formally executed >15,000 of their own troops at Stalingrad for various and sundry infractions....to say they were ruthless would be a slight understatement.
True, and this isn't just Hollywood. NKVD were very naughy boys.
The truth is concealed due to all the Left Wing radicals in Russia and here in the States.
Communism, Marxism, Leninism are their religious ideals and Stalin is their (false) "god" incarnate, the Dictator of the Proletariat.