I don't know if Koestler ever did any serious research into the Rajk-trial: Darkness at Noon
was written earlier & its hero is modeled after Bukharin.
The best account of the Rajk-trial (surprisingly little research btw, though the Times & NY Times did report about the case in 1949) comes from Hungarian emigre Francois (Ferenc) Fejto who was a friend of Rajk & who, w/ surprisingly astute observation analyzed the whole procedure & called it for what it was: a setup. If you read French, his article in the French journal L'Esprit is an essential read. it's in the 1949 Nov issue: pretty fast on the mark while French communists were still trying to convince themselves that Rajk actually did what he "admitted". In any case, if you're interested in that, email me.
(Btw his History of the People's Democracy is also a basic work on teh issue of Stalinism in Eastern Europe.)
