he is accused of "spying", that is: collecting information about things the tunisian government doesn't want other people to know and then give that information to foreign parties.

His job for the UN was to find out if tunisia is violating UN rules.

In other words, he did exactly what they are accusing him of, just that it isn't spying because tunisia have themselves decided to be a part of UN.

'Official researcher' would seem an unusually direct cover for a spy.