Huh? What book did you read? If you read Homage To Catalonia you would have seen that the Commies (usually the ones who DID NOT fight at the front) were the ones responsible for the imprisonment and execution of many of those fighting on the Republican side. Also Orwell showed how many journalists back then (and also now) covered up the purges and executions by the Communists.
And in Homage To Catalonia I saw many of the ideas that would come out later in Orwell's Animal Farm.