Five years ago, President Obama took the extraordinary decision to target Anwar al-Awlaki, a charismatic American-born imam turned Al Qaeda terror plotter, for taking the “lead in planning and directing efforts to murder innocent Americans.” Al Awlaki was killed by a drone strike in Yemen on September 30, 2011.

Al Awlaki wasn’t just an anti-American propagandist. He demonstrated a hands-on commitment to killing Americans. For example, Al Awlaki was in direct contact with Nidal Hasan before the Army psychiatrist went on a shooting rampage in 2009, killing 13 people at Fort Hood, Texas.

Al Awlaki also personally directed and supplied the explosives that Umar Farouk Abdulmutallab hid in his underwear and tried to detonate on an airplane from Amsterdam to Detroit on Christmas Day, 2009.

Al Awlaki began the Al Qaeda magazine Inspire, which includes articles like, “Make a Bomb in the Kitchen of Your Mom.”

Awlaki’s influence shows no signs of abating, thanks in part to the ubiquitous presence of his violence-inspiring sermons on the internet. In a report released just last week, the Counter Extremism Project (CEP) detailed 88 U.S. and European extremists who have been directly inspired by Awlaki’s calls to jihad.

Five years later, Al Awlaki’s influence shows no signs of abating, thanks in part to the ubiquitous presence of his violence-inspiring sermons on the internet. In a report released just last week, the Counter Extremism Project (CEP) detailed 88 U.S. and European extremists who have been directly inspired by al-Awlaki’s calls to jihad.

Most recently, New York and New Jersey bombing suspect Ahmad Khan Rahami included messages in praise of Al Awlaki in a notebook retrieved by U.S. law enforcement.

Sadly, he is simply the latest to fall victim to Al Awlaki’s incitement. CEP’s report indicates that virtually every major American-Islamic terrorist in recent years—Al Qaeda and ISIS adherents alike—were inspired by video and audio recordings of Al Awlaki’s sermons.

Last March, Orlando assailant Omar Mateen killed 49 people in the single deadliest gun attack on U.S. soil. Mateen was a known Awlaki follower and fan of his online “recruitment videos.”

Before killing 14 people with his wife last year, San Bernardino shooter Syed Farook regularly watched Al Awlaki’s lectures with his neighbor, sometimes for hours each day.

Mohammad Abdulazeez—the man who killed five U.S. servicemen in Tennessee last year—watched al-Awlaki videos prior to carrying out his attacks, as did the 2013 Boston bombers, the 2015 Charlie Hebdo attackers, the 2012 Times Square bomber, and the 2015 Garland shooters.

Al Awlaki’s lectures are ubiquitous on YouTube, for example, where a search for “Anwar al-Awlaki” produces nearly 70,000 hits.

Among them are Al Awlaki’s “Constants on the Path of Jihad” lecture, wherein he rhetorically asks, who among his listeners are willing to “terrorize the kuffar [non-believers].”

Other lectures urge listeners to carry out attacks against Americans as “jihad against America is binding upon myself, just as it is binding on every other able Muslim.”

It does not have to be this way. The ability now exists to remove, permanently, the most horrific al-Awlaki videos and messages from the internet, and thereby reduce his enormous potential to inspire further violence.

CEP and Dartmouth computer science professor Dr. Hany Farid has developed a technology, called eGLYPH, which can efficiently find and remove extremist content that has been determined to violate the terms of service of Internet and social media companies.

It works like this: Once a person identifies an image, video or audio recording for removal, the algorithm extracts a distinct digital signature from the content. That digital signature is then used to find duplicate uploads across the internet.

In the case of Al Awlaki, once his most noxious videos are flagged and removed, they would automatically be discovered and removed every time an upload was attempted.

In a 2010 New York Times interview, a former colleague of al-Awlaki—fellow imam Johari Abdul-Malik—said that Al Awlaki “is a terrorist, in my book” and cautioned shops not to carry even the earlier al-Awlaki CDs. According to Mr. Abdul-Malki, Al Awlaki’s lectures become “a gateway for the unsuspecting.”

The evidence clearly bears out his prediction. There is no longer an excuse for not addressing the continuing threat posed by Al Awlaki online. All that is missing now is a willingness to act.