The public line of the Obama administration is that no evidence has emerged to suggest bin Laden had high-level help inside Pakistan. Pakistan's Inter-Service Intelligence agency said bin Laden's long and comfortable existence in the country was an "intelligence failure."

But suspicions have increased following recent disclosures by one of bin Laden's wives in a police interrogation report that the Al Qaeda leader lived in five houses while on the run and fathered four children, two of whom were born in Pakistani government hospitals.

"I just find the idea that he lived in a place like Abbottabad without the ISI's knowledge strains credibility," said Shawn Gregory, director of the Pakistan Security Research Unit at Bradford University in the U.K. "It is ridiculous that he wasn't being protected."

Since the raid, Pakistan has tried to close one of the most notorious chapters in its history.