In Iran, Hamza’s mother Khairiah Saber urged the al-Qaida lieutenants there to take her son — now a teenager — under their wing. Hamza wrote to his father recounting the Islamic theology books he studied in detention, while expressing frustration that he was not among the jihadis in battle.

“The mujahedeen have impressed greatly in the field of long victories, and I am still standing in my place, prohibited by the steel shackles,” Hamza wrote in one of his letters found at Abbottabad. “I dread spending the rest of my young adulthood behind iron bars.”

But those shackles ended up keeping him and the other al-Qaida members safe as the U.S. under Bush and later President Barack Obama targeted militants across the Mideast in a campaign of drone strikes. Hamza’s half brother Saad escaped Iranian custody and made it to Pakistan, only to be immediately killed by an American strike in 2009.

“That probably saved (Hamza) that he was in Iran during that period where everyone else was being knocked off, detained,” said Tricia Bacon, an assistant professor at American University who focuses on al-Qaida and once worked in counterterrorism at the State Department. “It probably was one of the better places to be able to re-emerge at a later time.”