The CIA has released 470,000 files that were captured during the raid that killed al-Qaeda leader, Osama Bin Laden, in May 2011.

CIA Director Mike Pompeo said that he authorised the release of the massive trove of documents in the interests of "transparency" and "to enhance public understanding of al-Qaeda and its former leader."

"Today's release of recovered al-Qaeda letters, videos, audio files and other materials provides the opportunity for the American people to gain further insights into the plans and workings of this terrorist organisation," Pompeo said.

"(The) CIA will continue to seek opportunities to share information with the American people consistent with our obligation to protect national security."

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A spokesperson for the intelligence agency told Al Jazeera that the release of the documents was not in response to any legal request.

The files, which are almost entirely in Arabic, contained Bin Laden's personal journal and more than 18,000 files.

The trove includes approximately 79,000 audio and image files, which include practice reels for public speeches, and audio correspondence.

Among the more than 10,000 video files, are a video of Bin Laden's son Hamza as a young adult, "home videos," draft statements by Bin Laden, and al-Qaeda promotional material.

Some documents contained letters written by Bin Laden to his son Hamza instructing him to leave Afghanistan and travel to Pakistan after he obtains fake ID and other documents.

Others discussed issues, such as the validity of suicide bombings in Islam, particularly against civilians in Iraq.

Mergers between al-Qaeda affiliated groups in Libya, Yemen, North Africa, Egypt, and Central Asia, were also mentioned.

"The CIA's release of various records seized in the raid that killed Bin Laden will be of significant value to researchers and historians," said Washington, DC, lawyer Mark Zaid who specialises in national security and freedom of information requests.

"It also shows the value of congressional involvement in mandating declassification of records, as otherwise, it might have taken years before the public ever sees these documents" he added.

One document, labelled "top secret", revealed correspondence between Bin Laden and several named Saudi clerics through intermediaries.

Zarqawi and Maqdisi

Another document compared the ideology of former al-Qaeda in Iraq leader Abu Musab al-Zarqawi and his mentor, Abu Mohamad al-Maqdisi.

The letter described al-Zarqawi as practical and reacting to the things on the ground sometimes without thinking of the consequences or long term.

Al-Zarqawi was criticised for "taking things personally" and using violence without thinking of its impact on the greater cause of Muslims.

Al-Maqdisi, on the other hand, was described as a "strategic thinker" who does not advocate the use of violence.

Al-Qaeda in Iraq would later subsume other groups to form the Islamic State of Iraq and the Levant (ISIL, also known as ISIS).

Al-Maqdisi told Al Jazeera that he was not surprised that bin Laden was reading his work.

"This information has long been known, so there are no surprises there," he said.

"These documents are indispensable," Bob Baer, a former CIA case officer and expert on al-Qaeda, told Al Jazeera from Colorado, US.

"We do it so infrequently, but anyone who understands national security understands it is absolutely crucial to understand your opponents' grievances."

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