Leon Trotsky, co-leader of the October 1917 Revolution, was assassinated in Mexico on August 20, 1940. Security and the Fourth International, launched by the International Committee of the Fourth International launched in May 1975, was the first major investigation into the circumstances of his murder.

This volume, published in 1981, presents documents from the investigation’s first year, which uncovered abundant and long-concealed evidence of GPU penetration of the Trotskyist movement. These revelations exposed how Stalin’s agents orchestrated the murders of Trotsky, his son Leon Sedov, and comrades including Rudolf Klement, Erwin Wolf, and Ignace Reiss, as part of the broader counterrevolution that followed the Moscow Trials.

The World Socialist Web Site will be publishing sections from this volume over the coming weeks, to accompany Lecture 5-7 of the Socialist Equality Party (US) 2025 Summer School, held between August 2-9, 2025. An epub version of the text is available for purchase through Mehring Books here.

• Part 1: An Open Letter to All Workers Organizations
• Part 2: Introduction to the 1981 Volume
• Part 3: Statement of the Workers League
• Part 4: Statement of the Workers Revolutionary Party
• Part 5: Correspondence of the International Committee
• Part 6: How the GPU Murdered Trotsky
• Zborowski is planted by the GPU
• Sedov is killed in the clinic
• Stalin’s death warrants
• Murder in Mexico
• The strange case of Robert Sheldon Harte
• The assassin is silent
• Jack Soble: master spy
• Zborowski switches to New York
• Dr. Soblen’s spy team
• Beria’s network in the USA
• Trotsky’s secretary testifies
• Mrs. Dallin tells a strange tale
• Kravchenko “chooses freedom”
• A Red general unmasks Zborowski
• Mrs. Dallin and the NKVD
• The FBI picks up Zborowski
• The role of Joseph Hansen
• The cover-up takes shape
• We charge Joseph Hansen
• Two Answers to Hansen’s Silence