I don't want to comment on who killed Zia however brigadier Ijaz is a controversial figure and a corrupt person. Don't believe every thing he is saying.
'en.wikipedia.org/wiki/Ijaz_Shah#Role_in_Benazir.27s_Assassination_Attempt
there was a us ambasador on the plane aswell, but theres no mention of him
Also something makes me feel that this is what the world (open source) really believes:
This wasnt the first or even the last time US was handed over a fait accompli.
Some of the relevant questions could be:
(1) Who were the people who benefited the most from Zia's death?
(a) en.wikipedia.org/wiki/Brigadier_Imtiaz
(b) en.wikipedia.org/wiki/Mirza_Aslam_Beg#Accusation_of_role_in_Zia.27s_death; or en.wikipedia.org/wiki/Mirza_Aslam_Beg#Solidarity_with_Osama_bin_Laden
(2) What was it that actually happened after Zia went?
(2a)en.wikipedia.org/wiki/Hamid_Gul#Iranian_front; or en.wikipedia.org/wiki/Hamid_Gul#Turning_Against_America; or
en.wikipedia.org/wiki/Hamid_Gul#Solidarity_with_Osama_bin_Laden; or
en.wikipedia.org/wiki/Hamid_Gul#Accusation_by_Benazir_Bhutto
(3) What was it that could not happen when Zia was there?
General Zia-ul-Haq died in a plane crash on 17 August 1988 en.wikipedia.org/wiki/Kashmir_conflict#Rise_of_militancy_since_1989
(4) What was it that Zia could have been counting on for his survival and that actually did not come to his rescue when the time came? en.wikipedia.org/wiki/Zia-ul-Haq%27s_Islamization#Land_Reforms; or en.wikipedia.org/wiki/Hudood_Ordinance
Also many people, all thru history, blamed Zia for all the ills in Pakistan, but can an infection actually happen if the bodies immune response is strong.
Or is it, that the body actually asked for the infection?