:::: AnonMoos - It wasn't Amin al-Husayni and the Chairman. He was the Chairman.  I was grammatically incorrect and on further checking... 
 :::: the Arab Higher Committee ceased to exist 27th September 1937 when it was outlawed by the British. 

 :::: I now suggest - "Amin al-Husaynis had collaborated with Nazi Germany during World War II, when he longer represented the Palestinians in any official capacity after his dismissal from the office of the Grand Mufti of Jerusalem in 1936 (ref) and after the Arab Higher Committee was outlawed by the British on 27th September 1937." 
 
 :::: The second part of your post is irrelevant to the nature of the suggested change. Ahmad Shuqeiri"The neutrality of this article is disputed"