3. Boris Berezovsky
Boris Berezovsky was one of the wealthy Russian oligarchs and a government official. He was directly open about his opposition to the president of Russia, Vladimir Putin.
In the late 2000, Berezovsky was supposed to come back to Russia for questioning by the Russian Deputy Prosecutor General but he did not return. He stayed abroad and moved to the UK where he was granted a political asylum in 2003.
He apparently had secret information that he was going to make public. The secret was about the death of Alexander Litvinenko. He had also threatened to bring down Putin by force.
The British police has had to investigate several alleged assassination attempts against him during his stay in the UK. But in March 2013, he was then found dead in his house, in his own bathroom.
It was reported to be a suicide by hanging as there were no signs of struggle found. But the coroner recorded his death as open verdict saying the death was very suspicious and there were no evidence indicating that he intended to take his own life.