Reader Jeremy Putley advises that the KGB's use of Thallium as a poison goes back decades (as generally does its tradition of killing):

A

The following passage from a 1988 book, “A Higher Form of Killing: The Secret History of Chemical and Biological Warfare” by Robert Harris and Jeremy Paxman, describes the experience of Nikolai Khokhlov, formerly a captain in the KGB, almost fifty years ago.

“Khokhlov became a frequent speaker at anti-Soviet gatherings, where his experience as a KGB agent lent authority to his attacks on the Soviet system. But while at a speaking engagement in Frankfurt in September 1957, Khokhlov became violently ill. His face became covered in black, brown and blue lumps, his eyes oozed a sticky liquid, lumps of hair fell from his head. Two days later his German doctors decided that death was imminent. Khokhlov was transferred to an American military hospital, where six doctors began a desperate battle to save his life. They knew little about what had poisoned Khokhlov, but by constantly changing his blood, and with huge doses of cortisone, steroids, vitamins and experimental drugs, they managed to keep him alive. Gradually, Khokhlov recovered. Only later were American experts able to deduce from analysis of the course of Khokhlov’s illness that he had been poisoned by the insertion of highly radioactive metal fragments [thallium] into his food supply.”

B

The following is a newspaper report from Nigeria:

Another political refugee (and former KGB agent) was Nikolai Khokhlov who was haunted by the Russian government for listening to his conscience not to eliminate an innocent man. Though he had no unusual encounter with any person, Khokhlov, while participating in a convention at Frankfurt, German, became ill and later collapsed. Regaining consciousness, he suffered violent nausea that doctors treated as acute gastritis. But the treatment was unavailing. On Khokhlov's fifth morning in a Frankfurt hospital, a nurse entered his room and stared at him in transfixed horror. "What is it?" Khokhlov demanded. Then he looked in a mirror with a horror of his own. Hideous brown stripes, dark splotches and black and blue swellings disfigured his face and body. A sticky secretion oozed from his eyelids, and blood seeped through his pores; his skin felt dry, shrunken and aflame. At the mere touch of his hand, a shock of his hair fell out. An eminent professor of medicine suspected that he had been poisoned with thallium, a rare toxic metal. However, treatment with thallium antidotes had no effect. Tests showed that Khokhlov's white corpuscles were being swiftly and fatally destroyed, his bones decaying, his blood turning to plasma, and his saliva glands drying up. That night doctors said his case was hopeless and death imminent. Following pleas from the man whose life he had saved, Khokhlov was transferred to a US military hospital in Frankfurt. Protected constantly by armed guards, a team of six American physicians now began a duel with some unknown death specialists. Around the clock, they gave him massive injections of cortisone, vitamins, steroids, ACTH, and experimental medications, while keeping him alive with intravenous feeding and almost continous blood transfusions. An anesthesiologist stood by, preparing solutions for Khokhlov's mouth which was devoid of saliva, and otherwise trying to ease his agony. More specialists arrived for consultation and analysis and still newer drugs were rushed to Frankfurt. For a week, the supreme resources of American medicine barely kept Khokhlov alive. Subsequently, a famous American toxicologist, who studied the medical records in consultation with colleagues, found the answer. Khokhlov was poisoned with thallium that had been subjected to intense atomic radiation, which causes the metal to disintegrate into tiny particles. Introduced into his body through food or drink, the radioactive particle disintegrated completely and permeated his system with deadly radiation.