What happened to Alexander Litvinenko is still a mystery.
An astonishing case with him being injected with a dose of radiation.
'Hunting the KGB Killers'

The ‘Litvinenko Incident’ is where the ex Russian spy was killed with a radioactive substance in London. Ten years later, investigators and relatives at the time expose unexpectedly bring to light details of how the assassination was carried out.

A high concentration of Polonium was detected coming from the hotel room and sushi restaurant where a KGB official who met with Litvinenko stopped by. Surveillance camera images also deepen the suspicion. British investigators flew to Moscow but suffer from unexplained diarrhea traced back to ingenious sabotage on the Russian side ... and when the British government concluded from the 2006 case that "President Putin is involved”, the “careless nonsense" of the Spy community also emerged. Similar cases are still going on ... What can the world learn from this?

This incident just happened earlier this year.
"Russian spy: Nerve agent 'used to try to kill' Sergei Skripal"

Perhaps they tried to secretly assassinate behind the scenes like in a movie?
Mafia spreading the message “don’t go against us” with murder still goes on.