4. Alexander Litvinenko
Alexander Litvinenko was a former spy or officer for the Russian Federal Security Service or the FSB for short. He fled to London from a court prosecution in Russia on charges of ordering the assassination of a Russian tycoon with some other officers against their authority.
He was then granted asylum in the UK. There he worked as a journalist and a consultant for the British intelligence services. He wrote two books criticising and exposing things that happened surrounding the issue on how Vladimir Putin came to power.
It was on the 1st November 2006 that Litvinenko suddenly fell ill and got hospitalised. He died 3 weeks later and was found to be poisened with Polonium 210, a very rare isotope, which gave him radiation poisoning. The radiation poisoning degrades the cells down to its DNA and other key molecular structures.
Alexander Litvinenko wrote a letter on his deathbed and blamed Vladimir Putin for the poison. But no hard evidence were found on who put the poison there or even how it got there. Their tracks were covered completely.