Over the years, political critics, turncoat spies and investigative journalists have been killed or assaulted in a variety of ways

Former KGB agent died in London in 2006 after drinking tea laced with radioactive material; UK charging 3rd suspect in 2018 nerve agent attack on ex-Russian agent Sergei Skripal

Contradicting Russian doctors, who blamed a metabolic disorder, German medical officials say Putin critic was probably hit by substance that targets central nervous system

Kremlin denies resistance to transfer was political; dissident to be treated at specialist facility after suspected poisoning