This is the best documentation on the subject. A friend of mine bought the French version for me when we were in Paris. The English version has been available for 20 years.
The authors were academics. The first major section is an indictment which could be used in international courts to bring the perpetrators to the bar.
The Black Book of Communism
The Black Book of Communism: Crimes, Terror, Repression is a 1997 book by Stéphane Courtois, Andrzej Paczkowski, Nicolas Werth, and several other European academics documenting a history of political repression by Communist states, including genocides, extrajudicial executions, deportations, and killing populations in labor camps and artificially created famines.
Thanks for the info!