This article starts off with meeting between Graham/Goss and Mahmoud Ahmed, or 'Mehmood Ahmed' as it is spelled some other places. Also, what is the reason spellings always differ so much?
We have the same with a lot of names in the west as well, Jacob, Jakob, Yakob, Yakov, Jakub, Jakup etc.
If I'd have to guess, Mehmood is what is used in Pakistan, reflecting local pronunciation, whereas Mahmoud is the more traditional Arabic translation of the name (which is Arabic).