The South African passport carried by senior al-Qaeda militant Fazul Abdullah Mohammed was a forgery, South African officials say.
Mr Mohammed was reported killed last week in Somalia in a shootout with police in the capital, Mogadishu.
Somali sources said he was carrying $40,000 in cash and a passport in the name of Daniel Robinson when he died.
Experts say corruption in South Africa has made it easy for terrorists to get documents there.
South African officials say that following extensive domestic and international media coverage of the report that the passport was South African they launched a thorough investigation.
After receiving a copy of the passport, they checked the ID number that appeared on the document.
Officials said checks were also made to determine when Mr Mohammed entered or left South Africa.
They now say "without equivocation":
The passport was not issued by any lawful South African authority charged with the responsibility for the issuance of passports
No correlation existed between the ID number appearing on the fake passport and the fake passport number
The South African Movement Control System had no record of any movement in or out of the country at any port of entry by the militant using the fake passport.
The Minister of Home Affairs, Nkosazana Dlamini Zuma, welcomed the report and expresses the hope that the outcome would lay the issue of the security of South African documents to rest.
Security experts have been warning for years that corruption in South Africa is allowing terrorists to get documents to hide their identities, making it easier to travel.
Scott Stewart, a former intelligence agent with the US State Department, told the Associated Press that South Africa is a place where "you could show up, give the right guy several hundred dollars, and walk away with... a passport".
Mr Mohammed was the most wanted man in Africa, with a $5m (£3m) bounty on his head.
He was suspected of having played a key role in the 1998 US embassy bombings in East Africa, which killed 224 people.
Born in the Comoros islands in the early 1970s, Mr Mohammed is believed to have joined al-Qaeda in Afghanistan during the 1990s.
In recent years, he is thought to have joined other foreign militants in Somalia fighting fought alongside al-Shabab, which declared allegiance to al-Qaeda in 2010. It said reports of his death were untrue.
Source: BBC News