As President of the national diamond traders organisation in 2000, Alphonse Ngoy Kasanji played a central role in the Nkogas diamonds story , a 267,82 carats diamond the size of an orange and pure as water from the rocks, which is documented in the book "Chasse au Diamand au Congo/Zaïre " by By Laurent Monnier, Bogumil Jewsiewicki, Gauthier de Villers who write:
"The case at the time should be seen in the context of increasing hostility of many Baluba's of Kasaï against those in power which are the baluba's from Katanga"
Minister of finance Mawampanga Mwanananga at the time claimed that the diamond was state property, Alphonse Ngoy Kasanji was arrested and spent 54 days in prison.
Alphonse Ngoy Kasanji instructed his Belgian Lawyer, Geert Versnic, to make clear to diamond traders in Antwerp that anyone who would buy the diamond would do it at his own risk. In the meantime civil society in Kasaï tried to organise a protest, which was prevented by Zimbabwean soldiers.