An FBI agent reviewed a popular 1951 book about the nature of mass movements in an attempt to figure out how a young blogger who published incendiary posts about violent jihad became "radicalized," according to hundreds of pages of new FBI files obtained by VICE News.

The North Carolina-based blogger, Samir Khan, was a founding editor of an online magazine produced by al Qaeda in the Arabian Peninsula. He was killed with the radical preacher Anwar al-Awlaki — who was also a US citizen — in a CIA drone strike in Yemen in 2011. The Obama administration sought approval from the Justice Department to assassinate al-Awlaki.

On December 16, 2008, the FBI agent submitted a report to Khan's FBI file stating that he read Eric Hoffer's social psychology book The True Believer "solely with subject Khan in Mind."

"In an attempt to understand why Samir Khan has chosen the path that he is on, writer reviewed Eric Hoffer's The True Believer, which was written as a general overview of the nature of mass movements (not any one in particular)," wrote the agent who worked at the FBI's Charlotte, North Carolina field office. "All quotes below come from Hoffer's book."

The FBI, however, redacted the excerpt from the book, which first gained popularity in the 1950s when President Dwight D. Eisenhower championed it, and which continues to be read today. The agent added in his report, "In exploring Khan's frustration more in-depth, case agent offers the following." The FBI redacted what followed.

The 247 pages of heavily redacted files on Khan are the fourth installment of records the FBI began turning over to VICE News late last year in response to a Freedom of Information Act (FOIA) request. The bureau said it withheld more than 500 pages of documents from this cache citing a wide range of FOIA exemptions that include national security, law enforcement proceedings, and law enforcement techniques and procedures. Still, the files provide rare insight into the FBI's attempts to capture Khan before he traveled to Yemen.

Khan was born in Riyadh, Saudi Arabia in 1985, and grew up in Queens, New York. He started blogging about jihad, according to the FBI files, in 2004, the year he moved with his family to Charlotte, North Carolina. The FBI first learned of Khan in November 2006, when the 20 year old started publishing blog posts about his support for an Islamic organization linked to terrorism and, according to the FBI documents, advocated for the beheading of journalists. Two months later, the FBI opened a file on Khan and actively collected intelligence about him.

The new batch of documents contains what appears to be the government's first official documentation of when it learned that Khan had connected with al-Awlaki: November 2008. The file says, "Khan has been in contact with Anwar Aulaqi, an FBI San Diego subject who was acquainted with two of the 9/11 hijackers [of American Airlines Flight 77] while serving as the Imam at a mosque in San Diego, California." The rest of the file is redacted.

After the FBI agent submitted the report, Michael Heimbach, the assistant director of the FBI's counterterrorism division, sent an urgent memorandum to Patrick Rowan, the deputy assistant attorney general at the Justice Department's National Security Division. Much of the November 14, 2008 memo, classified as secret, was redacted. It contained the subject line, "Request for Attorney General" and a subheading, "Basis for Request." Left partially unredacted was background about Khan and his fiery blog posts and the media attention he attracted.

Al-Awlaki moved to San Diego from Denver in 1996. While living there he was investigated by the FBI over his alleged links to Hamas. The Khan files show that about two months after the FBI established that he began communicating with al-Awlaki, the title of Khan's file and the classification code was changed due to his contact with the propagandist. The discussion surrounding al-Awlaki also provides some rare insight into the Obama administration's concerns about the radical preacher.

"As instructed by FBIHQ [FBI headquarters]/CTD [counterterrorism division], captioned case is being reclassified as a 415A [international terrorism] due to the fact that subject is in direct contact with Anwar Aulaqi, subject of a San Diego Division case. Aulaqi can be considered an alleged senior Al Qaeda leader, or, at the very least, an alleged Al Qaeda facilitator who is in contact with senior Al Qaeda leadership," states a January 8, 2009 FBI file.

The files show that Khan was also under physical surveillance by the FBI. On January 6, 2009, an FBI agent submitted a newspaper article about a rally that Khan participated in, along with a photo. The subject of the rally is unclear, as details about it were redacted from the FBI file. But around that time there were several pro-Palestinian rallies taking place in Charlotte. Another file shows an FBI agent requesting permission on January 29, 2009 to travel to the Columbia, North Carolina field office to conduct surveillance on Khan.

Although he was killed in a drone strike — Attorney General Eric Holder said Khan wasn't the intended target — the FBI by late 2008 became more determined to prosecute Khan on material support for terrorism and conspiracy charges. (The bureau also considered recruiting Khan as a source.) But it wasn't the bureau's top priority, the files reveal.

"It was discussed that investigators should approach this case with the idea that it needs to have an ending, ideally the prosecution of Samir Khan," the FBI Charlotte case agent wrote on December 4, 2008. "The reason for this is because Khan is becoming more radical, and although working this case simply to gain intelligence on Khan's contacts is certainly an option, it is the investigative team's view that all work done in this case should be focused towards finding a resolution, i.e. a disruption via arrest/prosecution.

The statements by FBI agents in the files indicating the bureau wanted to gather intelligence from people with whom Khan communicated suggest that the files likely contain information about Mohamed Osman Mohamud, a naturalized US citizen from Somalia who was sentenced to 30 years in prison last October for plotting to bomb a Christmas tree lighting ceremony in Portland, Oregon in 2010. FBI agents set up Mohamud; what he thought was a live bomb to blow up the tree lighting ceremony was actually a fake.

Court documents in Mohamud's case showed that he began exchanging emails with Khan in February 2009 when he was 18, and contributed articles under a pseudonym to the al Qaeda magazine Khan edited, called Inspire. There are numerous files dated February 2009 about Khan's contacts, the details of which were redacted, but notations that included Somali individuals.

However, one file from February 2009 shows that an FBI counterterrorism agent sent a report to the Charlotte field office to report that the bureau's Public Access Center Unit received an anonymous tip on its "Internet Crime Complaint Center" website claiming that Khan made a death threat against a Sarasota, Florida private investigator, whose name was redacted from the FBI files. A news report about the incident, however, revealed that the private investigator is Bill Warner, who allegedly was responsible for shutting down Khan's blog.

"May Allah send a hurricane over his house so that he can be wiped out, humiliated," Khan wrote in a blog post, which the FBI underlined for emphasis in its February 17, 2009 report about the death threat.

Yet for all the concern the FBI showed about Khan, agents still did not have enough evidence on him to warrant an arrest. Nor did the FBI believe that Khan posed an immediate threat to national security. Much of the concern the FBI showed in the unredacted portions of the files was attributed to Khan's writings about jihad and his support for al Qaeda. But agents believed Khan's growing radicalization could pose a larger threat to national security if he was not stopped.

"In his online blog, Khan has stated his desire to bring about the Islamic Caliphate and that he feels the West is a hypocrisy," an FBI agent at the Charlotte field office wrote in February 19, 2009 report submitted to Khan's file. "As this investigation has progressed, has revealed that Khan has become more radical, more religious, and is increasing his association with nefarious individuals."

Still left unexplained is how Khan was allowed to leave the country and travel to Yemen later in 2009 without incident. The FBI did not respond to requests for comment.