Without internet or phones, Osama's hideout was cut off from the outside world. Not even senior al Qaeda commanders knew their leader's whereabouts. But he still needed a way to get his messages out, and for that he relied on a handful of trusted couriers. It was one courier in particular that proved the linchpin in Sunday night's operation that killed the al Qaeda leader.

Photos: Inside bin Laden's Compound

Shortly after the Sept. 11, 2001, terrorist attacks, detainees told CIA interrogators about an especially important courier who went by the name Abu Ahmad al-Kuwaiti. A series of subsequent interrogations, including one of Khalid Sheikh Mohammed, confirmed the courier's importance. In 2004, al Qaeda operative Hassan Ghul revealed that the courier was close to Faraj al-Libi, who replaced Mohammed as al Qaeda's operational commander after Mohammed's arrest. A year later, al-Libi himself was captured, and he protested so adamantly that he'd never heard of al-Kuwaiti that the CIA took it as further evidence that he was their man.

According to a 2008 Guantanamo prison document obtained by WikiLeaks, detainees gave interrogators a patchwork of information about the courier: He was a Kuwaiti-born man who helped al Qaeda members and their families find safe havens, sometimes travelled with bin Laden, and may have helped train Maad al Qathani, the alleged “20th hijacker.” Qathani told interrogators that al-Kuwaiti gave him computer training when he worked at al Qaeda's media house in Kandahar. The courier was “a senior al Qaeda facilitator and subordinate” at the time. The Guantanamo documents also say that Qathani told interrogators that the courier was seen accompanying bin Laden in Tora Bora just before the U.S. lost the al Qaeda leader's trail.

The revelation that information leading to the courier's identity was gleaned from CIA interrogations has been taken by some as a vindication of the agency's harsh interrogation techniques.

The revelation that information leading to the courier's identity was gleaned from CIA interrogations has been taken by some as a vindication of the agency's harsh interrogation techniques. “I would assume that the enhanced interrogation program that we put in place produced some of the results that led to bin Laden’s ultimate capture,” said Vice President Dick Cheney. “But I’m still—I need to know more.” Others pointed to the usefulness of surveillance in the search for bin Laden. Details of the hunt are still emerging, but early reports say that Mohammed opened up not during his infamously frequent waterboardings, but three years later during routine questioning. The case is less clear with Qathani, who reportedly spoke about the courier after being subjected to humiliating and brutal interrogation techniques, including being forced to perform dog tricks while on a leash and subjection to cold temperatures that twice required his hospitalization.

In any case, the detainees gave the CIA only snippets of information about the courier: not his real name or his whereabouts. A Guantanamo document even quoted a detainee as saying he was killed during the U.S. invasion of Afghanistan. Finding that the trail was going cold, CIA operatives went into the field, and eventually came up with the courier's family name, which they then used to intercept emails and calls from his family to anyone in Pakistan. Eventually they got his full name: Sheikh Abu Ahmed.

The next break in the case came in the middle of last year, when al-Kuwaiti called someone being monitored by U.S. intelligence, giving them the general area in which to search for bin Laden's lair. Pakistani agents working for the CIA spotted him driving his white Suzuki near Peshawar and took down the license number. After weeks of surveillance, al-Kuwaiti was tailed to the compound in Abbottabad, beginning yet more weeks of intense debate over whether bin Laden was in the house, and what to do about it.

Reports differ as to whether al-Kuwaiti was killed in the raid. One U.S. official says two of the three men killed at the compound in addition to bin Laden were couriers, but declines to identify them. The New York Times reported that one of the slain men was bin Laden's son, Hamza, and the other two were the courier and his brother. CNN was unable to confirm whether al-Kuwaiti was in the compound at the time of the raid.

Josh Dzieza is a reporter at The Newsweek Daily Beast company.