Osama Bin Laden
Osama bin Laden, terrorist mastermind behind the 9/11 attacks was killed in a US raid of his hideout in PakistanGetty Images

The fourth and final set of documents on Osama bin Laden released by the Obama administration show attempts by the al-Qaeda leader to continue to control the terrorist organisation despite being confined to his hideout in Abbottabad in Pakistan.

The latest series of documents which were found by agencies during the raid on his hideout in 2011 consist of letters to family, expense account entries and observations on world events. In a letter called the "third letter to Iraq", bin Laden describes the US occupation as "positive on all levels" for al-Qaeda and its agenda, "be it the enemy's human losses or the enemy's excessive budget depletion, or the fact that the Mujahidin were able to frustrate the enemy's plans for Iraq and for the whole region".

In other letters to his family, he mentions missing his sons Uthman and Muhammad but regretted that "our security situation does not allow us at this time to be together". He gave them detailed instructions to follow to ease their life on the run.

The letters also reveal the level of bin Laden's paranoia regarding the two boys. "If they inject you with a shot, this shot might be loaded with a tiny chip," he wrote in an undated letter. "The syringe size may be normal, but the needle is expected to be larger than normal size. The chip size may be as long as a seed of grain but very thin and smooth," he explained.

The mastermind behind the September 2011 attack on the US that killed nearly 3,000 people, bin Laden encouraged his subordinates to find new methods to cripple the West.

"If we cannot manufacture weapons like the weapons of the Crusader West, we can destroy its complicated industrial and economic system and exhaust its forces that fight without faith until they escape," he wrote in a letter to a fellow militant, soon after the attack.

"Therefore, the Mujahidin had to create new methods that no one from the West can think about, and one of the examples of this creative thinking is using the airplane as a powerful weapon, like what had happened in the blessed attacks in Washington, New York and Pennsylvania."