Then Don't Send Loose Cannons on Diplomatic Missions

The UN High Commissioner for Human Rights, Navi Pillay, is objecting to Israel's expulsion of Richard Falk, saying that, ""it is the responsibility of states to cooperate with the independent UN experts appointed by the UN Human Rights Council."

He's correct, of course, just as, for example members of the UN have an obligation not to appoint people who are batsh%$ insane to be their Ambassadors, so there is an obligation to criticize Bush and His Evil Minions^™ for appointing John "The Mustache of Doom" Bolton to the UN.

Unfortunately, Richard Falk has no more control of his tongue than did the 'Stache.

The man is an agent of a diplomatic organization on a fact finding mission, but he has made public statements which show that he should not be trusted with anything managing a Popsicle stand (or an academic department):

• Support for the 911 conspiracy theorists.
• Saying that, ""the depiction of [Khomeini] as fanatical, reactionary and the bearer of crude prejudices seems certainly and happily false ... To suppose that Ayatollah Khomeini is dissembling seems almost beyond belief. ... Having created a new model of popular revolution based, for the most part, on nonviolent tactics, Iran may yet provide us with a desperately-needed model of humane governance for a third-world country."
• Describing Israeli actions in the disputed territories as a Holocaust.
• Asking to investigate Palestinian abuses, but only to "insulate" the HRC from accusation of bias, which constitutes an explicit admission of bias on his own part.

(And that's just from a quick glance at his wiki)

Speaking as someone who was, and is, profoundly embarrassed by the fact that John Bolton is still given time in news shows and not relegated to circus acts, and horrified that snake oil salesman Benyamin Netanyahu was, and might be again, PM of Israel, the answer to the question is not to appoint equal and opposite nutjobs.

There are dozens, perhaps hundreds of people who could bring a dedication to the job, what's more, I've searched the net, and found no evidence that he either speaks Arabic or Hebrew, and at the very least, the investigator should be conversationally fluent in Arabic.

If an investigator cannot speak the language, it is very difficult for them to investigate. To rely on representatives of one government or the other to supply translators is to place a filter on on communications by the party supplying the translator.