• Ahmad Khan Rahami is in many ways quite typical of jihadist terrorists in the United States since 9/11, writes Peter Bergen.
• He is an American citizen, not a foreigner, a refugee or a recent immigrant, Bergen notes

Peter Bergen is CNN's national security analyst, a vice president at New America and a professor of practice at Arizona State University. He is the author of "United States of Jihad: Investigating America's Homegrown Terrorists."

(CNN)Ahmad Khan Rahami, the suspect in this weekend's New York City and New Jersey terrorist attacks, is in many ways quite typical of jihadist terrorists in the United States since 9/11.

He is an American citizen, not a foreigner, a refugee or a recent immigrant.

That is overwhelmingly the profile of the approximately 360 jihadist terrorists who have been indicted or convicted in the States since 9/11 of crimes ranging in seriousness from sending small sums of money to an overseas terrorist organization to murder. According to research by New America, 80% of these militants are American citizens or legal permanent residents.

They are also not the young hotheads of popular imagination. Their average age is 28, a third are married and a third have children. Rahami, age 28, is married and has a daughter.

FBI Assistant Director William Sweeney said Monday there is no evidence that Rahami was part of a cell, which also makes him also a typical American terrorist. Every lethal terrorist attack since 9/11 has been carried out by a so-called "lone wolf" or a pair of terrorists who were not part of a larger cell.

Indeed, in many ways Rahami is almost exactly like Omar Mateen, who killed 49 at an Orlando nightclub in June. Mateen was a 29-year-old married father and an American citizen of Afghan descent born in New York who carried out his plot by himself.

The bomb that went off in the Chelsea neighborhood this past weekend, injuring 29, is the first jihadist terrorist attack in Manhattan since 9/11.

Similarities to Boston bombing

The bomb device in Chelsea was almost identical to those used in the Boston Marathon attacks three years ago. Pressure cookers were used to house the devices; shrapnel was added to increase the lethality of the charges, and Christmas lights were used to initiate the explosions, according to law enforcement officials.

Terrorist groups have posted these recipes online.

Just as is often the case in school shootings, jihadist terrorists also study previous attacks and it's interesting to note the close match between the Boston bombs and the device used in Chelsea. Adding to the similarities to the Boston attack, a pipe bomb in Seaside, New Jersey, that Rahami is believed to have planted also targeted a running event, a Marine Corps charity run, but the device didn't injure anyone when it detonated on Saturday. Also, a notebook used by Rahami had jottings about the Boston bombers.

Of course, a major difference with the Boston Marathon bombing is that Rahami did not succeed in killing his victims. Unlike the Boston Marathon bombers, Rahami did not place his bomb directly on the street in Chelsea where it could inflict significant damage, but instead put his inside a dumpster, which largely contained the blast. This was a rookie error.

Rahami also used the peroxide-based bomb ingredient HMTD, which is rarely used by terrorists because it is both unstable and not as powerful as another peroxide-based explosive, TATP.

The US Department of Homeland Security says that one of the few terrorists in the States to have tried to launch an HMTD-bomb attacks is Ahmed Ressam, an Algerian al-Qaeda member living in Canada. Ressam built an HMTD-based bomb in Canada that he planned to detonate at Los Angeles International Airport in December 1999. Ressam was arrested at a U.S. border crossing before he could carry out his plan.

Terrorists have been more successful with the more powerful peroxide-based bomb TATP, which was used in the London transportation bombings in 2005 in which al-Qaeda directed suicide attackers killed 52 commuters.

Najibullah Zazi---like Rahami also a US citizen of Afghan descent---was also trained by al Qaeda in Pakistan in 2009 to build TATP-based bombs and, together with two American friends that he had grown up with in Queens, New York., Zazi planned to detonate these bombs in the Manhattan subway around the eight anniversary of the 9/11 attacks. Luckily, a tip from British intelligence led to the uncovering of Zazi and his two co-conspirators just days before they planned to launch their attacks.

The big question: Why?

The fact that Rahami almost perfectly fits the profile of an American jihadist terrorist doesn't, of course, answer the big question: Why would he attempt to murder complete strangers in the country that he had grown up in?

So far Rahami's precise motivations are still murky, but it's telling that in the notebook that he used he made notations about the American jihadist cleric Anwar al-Awlaki who, until he was killed in a CIA drone strike in 2011, was a key leader of al Qaeda in Yemen.

Lost in the intense coverage of the ISIS-inspired threat in the States is the continuing importance of Awlaki, whose sermons and writings about the importance of jihad have appeared in 99 jihadist terrorism cases since 9/11, according to New America's research. Awlaki was killed in a drone strike in Yemen in 2011, but killing the man turned out to be easier than killing his ideas; since his death al-Awlaki's writings and videos have turned up in 58 terrorism cases in the United States.

For the book "United States of Jihad: Investigating America's Homegrown Terrorists," I reviewed court records in hundreds of terrorism cases and spoke to family members and friends of terrorists, as well as to some of the militants themselves. American jihadists are generally motivated by a mix of factors, including dislike of U.S. foreign policy in the Muslim world. For many, embracing the ideology of Osama bin Laden or ISIS allowed them to become the heroes of their own story as well as actors in a cosmic crusade. For others a "cognitive opening" to militant Islam, was often precipitated by a personal disappointment or loss.

For each individual terrorist the proportion of these motivations varied. Take the Boston Marathon bombers who Rahami seemed to have emulated. Tamerlan Tsarnaev, one of the two brothers who carried out the marathon bombing was a non-practicing Muslim who only became an Islamist militant once his dreams of becoming an Olympic boxer faded. At the time of the attack, he was unemployed. On the other hand, his younger brother Dzhokhar never seemed to embrace militant Islam. He smoked marijuana, drank, and chased girls.

These stories of the two Boston Marathon bombers underline how hard it is to satisfactorily answer the question of why terrorists try to kill complete strangers.

Purely homegrown or trained overseas?

Now that Rahami is in custody, law enforcement will have a number of questions: Is he a purely "homegrown" terrorist, or was he trained overseas in Afghanistan or Pakistan, countries he visited often? Was the attack ISIS-inspired? If so, is there any indication Rahami was in direct touch with members of ISIS using encrypted communications? Or was he inspired or directed by some other jihadist group based in the Afghan-Pakistan region, such as al Qaeda or the Taliban?

Faisal Shahzad, an American citizen who had once worked at the Elizabeth Arden cosmetic company in Connecticut, was trained by the Pakistani Taliban in 2009 to carry out a car bomb attack in Manhattan. Luckily, he received only five days training and the bomb contained in a SUV that Shahzad parked in Times Square on a busy Saturday night on May 1, 2010 didn't detonate properly.

This was the last time that a terrorist who had been trained by a foreign terrorist organization attempted to carry out an attack in the United States, and since then we have seen attacks or attempted attacks in the States carried out only by "homegrown" terrorists.

That was the case this past weekend when Dahir Adan stabbed 10 people in a Minnesota mall. According to an American counterterrorism official, Adan had also grown up in the States.

Adan was quickly adopted by ISIS as a "soldier" of its so-called caliphate, the same nomenclature it used to describe Mateen after his attack in Orlando. Similarly ISIS embraced the perpetrator of the attack in July in Nice, France, that killed 84 people as a "soldier" of the caliphate.

There is no evidence these attacks were tied to ISIS in any way other than that the terrorist group supplied some degree of inspiration for them, and it only claimed responsibility for them after the fact. ISIS may also opportunistically claim Rahami as one of its soldiers.

Political fallout

There is already political fallout from the Chelsea attacks.

On Monday, Republican presidential nominee Donald Trump told Fox that such attacks would proliferate "because we're allowing these people to come into our country and destroy our country and make it unsafe for people."

In fact, Rahami is a naturalized American citizen who arrived in the States around age 7. Friends describe him as very Americanized, which is not surprising given the fact he has lived in the States for the past two decades.

And this is precisely the challenge US law enforcement faces. Despite the fact that the FBI says it is conducting 1,000 investigations of suspected Islamist militants in all 50 states, by the law of averages terrorists using low-tech weapons such as pressure bombs or legally acquired semiautomatic weapons will occasionally slip below the radar. (While initially officials said Rahami was not known to law enforcement for his militant views or actions, his father says he called the FBI two years ago when his son acted out violently.)

Going forward there were will be others like Rahami who will carry out low-tech terrorist attacks. Because they are American citizens, barring immigrants from Muslim countries or places where terrorism is endemic will do nothing to stem this problem.

These jihadist militants are already here.