[1] Carl Sternheim, a friend of the Pfemferts, met him during this period and described him as an extremely nice looking young man with light brown hair and blue eyes but who chain smokes and vividly explains that he goes through fifty of them every day".

[2] In 1932, he helped Trotsky create a political bloc with the anti-Stalin opposition inside the USSR and was in contact with some of its members like Ivan Smirnov, through the old bolshevik Eduard Holtzman, whom he called in his letters "the informant".

[5] After an acute attack of appendicitis in February 1938, Mark Zborowski, an NKVD agent who had posed as Sedov's comrade and friend, arranged to take him to a private clinic instead of a Paris hospital.

At the same time, Zborowski notified the NKVD that Sedov had been transported under an assumed name to the Clinique Mirabeau,[6][7] which was operated by a White Russian with connections to Soviet intelligence,[8] who performed an appendectomy.

In 1994, Pavel Sudoplatov, a lieutenant general in the NKVD who at that time was in charge of planning assassinations abroad, including the one of Sedov's father, claimed in his memoirs, Special Tasks, that Soviet agents played no part in his death.