Sudoplatov claimed to be responsible for Trotsky's assassination and was in charge of the Sooviet espionage effort to obtain the secrets of the atomic bomb from America and Great Britain. He set up a network of illegals who convinced Robert Oppenheimer, Enrico Fermi, Leo Szilard, Bruno Pontecorvoco, Alan Nunn May, Klaus Fuchs, and other scientists in America and Great Britain to share atomic secrets with the Soviets. He documents all sorts of dirty deeds and other than being quite out of character to not eliminate a defector, there does not appear to be any good reason to doubt him on this.
The circumstances of Krivitsky's demise are highly suspect, but there is a good chance that this might be the only such case for which they are not guilty. Maybe we can start a new conspiracy theory and claim that FDR ordered his elimination to get on the good side of Uncle Joe.
For extra credit someone may want to review the FBI report on Krivitsky: http://foia.fbi.gov/foiaindex/krivit.htm
Walter G. Krivitsky
570 pages
General Walter G. Krivitsky was found dead in the Bellevue Hotel in Washington, D.C., on February 10, 1941. Krivitsky was the former head of the Soviet Military Intelligence in Western Europe. Although his death was declared a suicide, some people were suspicious that the Soviets may have murdered him. No information was ever uncovered to prove his death was anything other than suicide