Vladimir Kara-Murza works for the pro-democracy group Open Russia and is openly critical of Putin's policy of assassinating people he isn't fond of. Last week Kara-Murza hospitalized with organ failure on the day he was to travel to the United States. He has been diagnosed with "acute intoxication by unidentified substance" and is in a life-threatening coma.
From the NYTimes:
On the Fox program, Mr. Trump said he respected Mr. Putin and hoped Russia and the United States could join forces to defeat Islamic terrorism. The host, Mr. O'Reilly, responded: "He's a killer though. Putin's a killer." It was unclear whether the characterization referred to the unsolved assassination of dissidents, muckraking journalists and opposition politicians or allegations of war crimes in Syria, Ukraine or Chechnya.
The Kremlin's spokesman, Dmitri S. Peskov, told reporters Monday that the description was "unacceptable, insulting."
The Soviet Union operated a secret laboratory to research untraceable poisons that were tested on condemned gulag prisoners, security service defectors have said.
Image by Leonidalekseev (Own work) [Public domain], via Wikimedia Commons
In 2015 Kara-Murza was hospitalized for two weeks for similar symptoms.