Former Russian spy Alexander Litvinenko was assassinated in 2006.

Litvinenko was assassinated with a tea that was laced with a radioactive poison called polonium. It was the only time this form of assassination has ever been recorded.

After an official investigation, it was found that the poison was administered by former KGB body guard Andrei Lugovoi and an accomplice, and that Russian President Vladimir Putin had "probably" ordered the assassination.

Litvinenko was a target because he was about to testify about Putin's government in a Spanish investigation. According to The Atlantic, this was a key moment in Russia's foreign relations, because Putin realized what he could get away with.