In case after terrorism case, from the Fort Hood, Tex., shootings to the Boston Marathon bombing and now to the slaughter in San Bernardino, Calif., the inflammatory videos and bomb-making instructions of Anwar al-Awlaki, easily accessible on the Internet, have turned up as a powerful influence.
Four years after his death in a drone strike on the orders of President Obama, the question of what can and should be done about the digital legacy of Mr. Awlaki, the American cleric and propagandist for Al Qaeda, is being asked with increasing urgency. Killing him, it is clear, only enhanced the appeal of his message to many admirers, who view him as a martyr.
Pressure on Internet companies to take down his work is growing, because legal experts say the First Amendment would prohibit the government from ordering restrictions. With emotions running high after the most lethal terrorist attack on American soil since Sept. 11, 2001, there is widespread frustration among counterterrorism officials and independent experts at his continuing impact. But possible solutions are divisive and complex, raising a tangle of issues involving technology, national security, religion and freedom of speech.
On Friday, the Counter Extremism Project, an advocacy group based in Washington, called on YouTube and other platforms to permanently ban Mr. Awlaki’s material, including his early, mainstream lectures.
“His work has inspired countless plots and attacks,” said Mark D. Wallace, a former diplomat and homeland security official who is the project’s chief executive. “It’s hate speech. It should come down, period. Like child porn, it should be expeditiously removed.”
Mr. Wallace said the ban should cover not just violent jihadist material, but anything Mr. Awlaki recorded, including such popular works as his 53-CD set of lectures on the life of the Prophet Muhammad, widely excerpted on YouTube and other sites. Though not objectionable in itself, Mr. Wallace said, such material adds authority to the cleric’s later calls for violence.
“There are a lot of sources for the teachings of Islam that do not come from a man who became one of the world’s most notorious terrorists,” he added.
But Muslim activists and civil libertarians oppose such measures. Jameel Jaffer, deputy legal director of the American Civil Liberties Union, said the call to remove all Awlaki videos was “misguided.”
“Some people seem to think there’s a one-to-one relationship between watching these videos and carrying out terrorist attacks, but people watch these videos for all kinds of entirely legitimate reasons,” Mr. Jaffer said. Censoring them, he said, “would certainly make it more difficult for ordinary citizens to learn the motivations, grievances and worldview of those who call for violence against Americans.”
Muslim Advocates, a civil rights group in Washington, also rejected a ban. The group said in a statement that YouTube should remove material inciting violence regardless of its ideological or religious bent “and not make an exception based on people’s faith.”
The debate over Mr. Awlaki takes place against the backdrop of a broader tension between national security officials and Silicon Valley companies whose services are sometimes used by terrorists. Twitter, for example, now aggressively suspends the accounts of Islamic State supporters, who for many months have used the site to get their message out.
On Thursday, in the latest case, Mr. Awlaki was named repeatedly in the criminal complaint against Enrique Marquez, a neighbor of the husband and wife who killed 14 people and injured 22 in the Dec. 2 shootings in San Bernardino. Like many others who have embraced jihad, Syed Rizwan Farook, the husband, and Mr. Marquez spent hours listening to Mr. Awlaki’s lectures and poring over directions on making explosives in the Qaeda magazine he helped create, Inspire, according to the complaint.
While Mr. Awlaki’s material is found in many places on the web, perhaps the largest collection is on YouTube. With some 400 hours of video being uploaded to YouTube each minute, the company relies both on automated technology and on users to flag objectionable content, which is reviewed and sometimes removed.
YouTube said in a statement on Friday that it has “clear policies prohibiting terrorist recruitment and content intending to incite violence.” But it said it permits “videos posted with a clear news or documentary purpose.”
In practice, YouTube has done little to remove even Mr. Awlaki’s most provocative material. A search on YouTube for “Anwar al-Awlaki” on Friday produced 61,900 results, including nearly everything he recorded on audio or video in a long career. Some are explicit endorsements of attacks on the United States and on Americans, including “Call to Jihad,” which Mr. Awlaki recorded in 2010 while in hiding in Yemen.
But Mr. Awlaki is rare among jihadist ideologues for having produced a large body of mainstream material as well as Qaeda propaganda. And much of his work is subtly situated on the border between the two, said Alexander Meleagrou-Hitchens, a lecturer at King’s College London who wrote his doctoral dissertation on Mr. Awlaki.
For instance, the F.B.I. says Mr. Farook and Mr. Marquez listened to Mr. Awlaki’s lectures on “The Hereafter,” a series also praised on Twitter by Dzhokhar Tsarnaev, one of the Boston bombers. Nominally it merely explores the Islamic concept of paradise. But Mr. Hitchens said the lectures have helped jihadists “rationalize and come to terms with their own deaths, thus helping them prepare for attacks.”
The California men also listened to Mr. Awlaki’s lectures on Omar bin al-Khattab, an early hero of Islam, “who killed and conquered in the name of Islam,” Mr. Hitchens said. “He then suggests that Muslims should take direct lessons from this, and act accordingly.”
Mr. Awlaki’s influence in terror cases was noticed by F.B.I. investigators as early as 2006. But it became a public issue in late 2009, after Nidal Hasan, an Army major and psychiatrist who killed 13 people at Fort Hood, turned out to be a fan of the cleric.
In 2010, under pressure from Congress, YouTube said it was removing hundreds of Mr. Awlaki’s videos and would not tolerate “content that incites violence.” But a check some months later found the cleric’s most extreme material still available, and it has rarely gone missing since then.
Likewise, Inspire magazine, with its instructions for constructing bombs and mounting other kinds of attacks, remains widely available on multiple websites. Mr. Awlaki helped create the magazine in 2010 and ran it with the help of another American, Samir Khan, who was killed in the same drone strike that killed the cleric.
“The half-life of Awlaki’s message is amazing,” said Patrick M. Skinner, a former C.I.A. counterterrorism officer now with the Soufan Group, a security consulting firm. “It really is like plutonium. It’s toxic, and it doesn’t go away.”
Mr. Skinner said he’s not sure it’s possible to erase Mr. Awlaki’s material from the Internet, since his supporters can repost it on many sites in many countries. But he said that if YouTube and other popular sites take it down, “maybe young people would get distracted looking for it and fewer people would see it.”
There may be lessons from other kinds of illicit material. Facebook and other companies now use a Microsoft process called PhotoDNA to find and delete child pornography, and similar methods are used to take down copyrighted material.
Hany Farid, a professor of computer science at Dartmouth who helped develop PhotoDNA, said it would not be difficult to design software to find images of Mr. Awlaki or samples of specific audio or video footage.
“It’s not a technical problem,” he said. “It’s a policy issue. I think the speech and privacy issues are tricky. But to say there’s nothing we can do about it is cowardice.”
An earlier version of this article misidentified the technology that YouTube uses to find and delete child pornography. It uses its own proprietary technology, not PhotoDNA.