Philip Alston, a professor of international law at New York University and the UN's former special rapporteur on extrajudicial, summary or arbitrary executions.
He spoke to Al Jazeera about the need for an investigation follow the discovery of polonium on the personal effects of Yasser Arafat.
"It seems that when polonium is used, it has to be produced by a very major nuclear reactor. It can't just be bought on the market. It can't be done in the back of a garden ... So in this case, while no one has pointed the finger directly - the obvious suspicion would be that Israel was involved. Israel clearly has a major nuclear capacity; presumably the ability to produce polonium and one would hope that it would therfore have some sort of interest in an enquiry being carried out."