Instruct: Classify Amazon reviews into positive or negative sentiment
Query: addendum

Though I have not read this book about Radek, I wish to add this information as a follow-up to the previous review. It has been substantiated that both Radek and Sokolnikov were killed by fellow inmates in prison in 1939. See for reference "The Road To Terror: Stalin and the self-destruction of the bolsheviks, 1932-1939" by Getty and Naumov.