This important work is an investigation into the motivation of a group of middle-aged German policemen who became part of an extermination group on the Eastern front. Browning shows by specific examples that the notion that these men had to be forced to kill Jews is sheer mythology.
The historical record he uses is transcripts of interviews with these men when in the 1960's they were prosecuted by German courts. The profile that emerges is that these men who became mass murderers were in their late 30's, had no prior record of brutality and were given a chance to opt out of the shootings. Yet, 90 per cent killed. They killed face to face with their victims--men, women and children.
Why? Browning identifys a number of factors including the power of group conformity and cohesiveness and the effect of psychological distancing from the persecuted group.