In the autumn of 2010, he and his wife Marina Kalashnikova were treated in hospital in Germany for mercury poisoning in what they said had been an attempt on their lives by Russia's FSB, the successor to the KGB.
They left Russia and have lived in various countries, such as Ukraine, Poland, Estonia and now Germany.
[1] The case was compared with that of another former Russian security officer, Alexander Litvinenko,[2] who was murdered in London in 2006; he is believed to have been administered a radioactive polonium isotope.
The Kalashnikovs claimed that they were poisoned in hotels and private residences in Estonia, Ukraine, Poland, Russia and Germany.
Spokesman for the state prosecutor's office in Berlin told the AFP news agency: "There is no evidence that they were poisoned, at least in Germany.