A highly radioactive isotope of Polonium (Po-210) has been linked to high profile political assassinations including former Palestinian leader Yasser Arafat, former Turkish president Turgut Ozal, and former KGB officer and political refugee Alexander Litvinenko.
Polonium-210 occurs naturally in very small amounts from uranium decay, but is also produced artificially by showering bismuth with neutron radiation. The isotope has few practical uses other than as a static eliminator in some manufacturing processes. It is so toxic that as little as a microgram, if ingested, would be lethal within several days. The only known stockpiles of polonium-210 reside in major nuclear nations such as Israel, Russia, and the United States.