Osama bin Laden didn't want to publicly recognize the Somali militant group al-Shabab as a part of al-Qaida because it would bring extra attention from "enemies," but months after his death, al-Qaida and al-Shabab announced a formal merger.
In a letter to al-Shabab leader Mukhtar Abu Zubeyr, bin Laden's advised against such an announcement. It's unclear if the Somali militant actually received the letter. The document was among those seized in the May 2011 U.S. raid that killed bin Laden in Pakistan.
Bin Laden wrote that the world would eventually find out about al-Qaida's unification with al-Shabab, but that no one would be able to prove it absent an official announcement.
"If the matter becomes declared and out in the open, it would have the enemies escalate their anger and mobilize against you; this is what happened to the brothers in Iraq or Algeria," bin Laden wrote in the document, which was posted online Thursday by the U.S. Army's Combating Terrorism Center.
The second reason, bin Laden wrote, was that Arab "merchants" would more likely donate to Somali causes if the "mujahideen" were not publicly tied to al-Qaida. Bin Laden noted "some Muslims in Somalia are suffering from immense poverty and malnutrition" and that the country could use development aid.
The letter was dated Aug. 7, 2010. It appeared to be a response to a letter from Abu Zubeyr in which the Somali militant raised the subject of announcing a formal alliance.
Nine months after bin Laden's death in the U.S. raid, al-Qaida's new leader, Ayman al-Zawahri, released a video in which he gave "glad tidings" that al-Shabab had joined his terror network, an indication the new leader disagreed with bin Laden's approach to Somalia.
Bin Laden was hiding in a large house in the Pakistani town of Abbottabad and restricting his communication with the outside world to avoid detection by the U.S.
The terror chief would write his letters on his computer and store them on flashdrives which were then given to trusted couriers to take to the intended recipient. Nonetheless, it is not definitively known if Abu Zubeyr ever received this particular message from bin Laden.
Al-Shabab leaders had pledged allegiance to al-Qaida in the past, releasing a video in 2009 called "At Your Service Osama!" The same year, bin Laden released a video in which he made encouraging comments about the Somali insurgency.
Despite his advice against a public announcement, the letter appeared to indicate that bin Laden backed a merger with al-Shabab, saying that "unity" should be carried out through unannounced secret messaging.
The Somali militant group is not extensively discussed in the documents released this week, but there are several references that indicate bin Laden was not always pleased with the group's style of governance in Somalia and inflexible administration of punishments for certain crimes.
The formal announcement of unity between al-Shabab and al-Qaida appeared to be designed to give a boost to two groups who have been losing popular support and facing increasingly deadly military attacks.
Al-Shabab has faced increased pressure from African Union troops in Mogadishu as well as Ethiopian troops in western Somalia and Kenyan troops in the south. Al-Qaida, meanwhile, has seen its top leadership devastated by drone strikes in Pakistan.