Assassination of world leaders

Name(s): 
Cover-up of murder of top people
Nature 
Risk of violence and assassination is a daily threat of most world leaders. Apart from indisputable assassinations, there are suspicious circumstances around the deaths of many leaders of governments and organizations.
Incidence 
The death in 1961 of UN Secretary General, Dag Hammarskjöld, in an airplane crash, has never been satisfactorily explained, either as a genuine accident or foul play of some sort.
Broader 
Type 
(D) Detailed problems