His killer ( s ) remain unknown , but a link with Russia 's Federal Security Service is suspected .
Litvinenko was a Russian dissident and ex-agent , poisoned with radioactive polonium - 210 on 1 November 2006 , and who died 22 days later .
Litvinenko 's killer ( s ) remain unknown , but a link Russian Russia 's Federal Security Service is suspected .
Litvinenko was a Russian dissident and ex-agent , poisoned with radioactive polonium - 210 on 1 November 2006 , and who died 22 days later .