Tom Buergenthal. Here’s the pertinent part indicating the reason for his dissent:
Since I believe that the Court should have exercised its discretion and declined to render the requested advisory opinion, I dissent from its decision to hear the case.
My negative votes with regard to the remaining items of the dispositif should not be seen as reflecting my view that the construction of the wall by Israel on the Occupied Palestinian Territory does not raise serious questions as a matter of international law. I believe it does, and there is much in the Opinion with which I agree.
However, I am compelled to vote against the Court’s findings on the merits because the Court did not have before it the requisite factual bases for its sweeping findings; it should therefore have declined to hear the case.
In reaching this conclusion, I am guided by what the Court said in Western Sahara, where it emphasized that the critical question in determining whether or not to exercise its discretion in acting on an advisory opinion request is “whether the Court has before it sufficient information and evidence to enable it to arrive at a judicial conclusion upon any disputed questions of fact the determination of which is necessary for it to give an opinion in conditions compatible with its judicial character” [Western Sahara, Advisory Opinion, I.C.J. Reports 1975, pp. 28‑29, para. 46].
In my view, the absence in this case of the requisite information and evidence vitiates the Court’s findings on the merits.
Judge Buergenthal died just last year, a few weeks after his 99th birthday.