Simpson, who was shot to death by police, is far from the only American who who has been drawn to the black flags of ISIS as well as to the al Qaeda affiliate in Syria known as the Nusra Front.
They hail from across the United States and from a wide range of ethnic groups, which underscores the difficulty that law enforcement has in tracking them. They are relatively young; some are even teenagers. Given the fact that groups like ISIS have scant roles for women outside the home, women are surprisingly well-represented. These militants are also quite active on social media. This is something of a boon for law enforcement, as many of these militants are prolific posters on publicly available social media, which it is perfectly legal for the FBI and police departments to monitor.
The 62 are residents of 19 states: Alabama, Arizona, California, Colorado, Florida, Illinois, Massachusetts, Michigan, Minnesota, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Texas, Virginia, and Wisconsin.
Just one thing in common
There is no single ethnic profile for these militants: They are white, African-American, Somali-American, Vietnamese-American, Bosnian-American and Arab-American, among other ethnicities and nationalities.
An unprecedented number of American women are involved in the Syrian jihad compared to other such jihads in the past. More than one-fifth of the 62 Americans involved in Syria-related militant activity are women.
Women were rarely present, if at all, among jihadists in previous "holy wars" -- in Afghanistan against the Soviets in the 1980s, in Bosnia against the Serbs in the 1990s, and the initial insurgency in Iraq against the U.S.-led occupation more than a decade ago.
They're relatively young. A quarter are teenagers -- including five teenage girls, the youngest of whom is 15. New America found that the average age of individuals involved in Syrian militancy is 25.
The only profile that ties together American militants drawn to the Syrian conflict is that they are active in online jihadist circles. Fifty-three of the 62 individuals showed a pattern of often downloading and sharing jihadist propaganda and, in a smaller number of cases, carrying on conversations with militants abroad.
Militants in the United States today become radicalized after reading and interacting with propaganda online and have little or no physical interaction with other extremists.
This trend has been going on for the past several years. Maj. Nidal Hasan, for instance, who killed 13 at Fort Hood, Texas, in 2009, became radicalized largely through reading militant propaganda online. As an active officer in the U.S. military, he had, of course, little opportunity to physically meet with fellow militants.
Social media have dramatically accelerated this trend. Of the 62 individual cases that New America examined, there were no clear cases of physical recruitment by a militant operative, radical cleric or returning fighter from Syria or radicalization while in prison.
Instead, people self-recruited online or were sometimes in touch via Twitter with members of ISIS they had never met in person.
A representative case is that of 19-year-old Mohammed Hamzah Khan
of suburban Chicago. In the late summer of 2014, he purchased three airline tickets for flights from Chicago to Istanbul for himself and his 17-year-old sister and 16-year-old brother (who have not been named publicly because they were minors).
Khan had met someone online who had provided him with the number of a contact to call once he had landed in Istanbul who would help to get him and his siblings to the Turkish-Syrian border, and from there on to a region occupied by ISIS. Khan planned to serve in the group's police force.
Before leaving, Khan wrote a three-page letter to his parents explaining why he was leaving Chicago to join ISIS. He told them that ISIS had established the perfect Islamic state and that he felt obligated
to "migrate" there.
According to prosecutors, the three teenagers planned to meet up
in Turkey with a shadowy ISIS recruiter they had met online, known as Abu Qa'qa, and travel with him, most likely to ISIS headquarters in Raqqa, Syria.
They didn't make it. FBI agents arrested Khan and his two siblings
at O'Hare Airport in October 2014.
There is no evidence that Khan planned to commit any act of terrorism in the United States or elsewhere, and he failed in his goal of reaching ISIS, but he faces up to 15 years in prison for allegedly attempting to provide "material support" to ISIS in the form of his own potential "services." He has denied the charge.
Why would the Khan teenagers, from a comfortable, middle-class family in Chicago, be drawn to Syria and to ISIS?
In the minds of ISIS recruits, the group is doing something of cosmic importance that in their view is sanctioned by Allah: defending Sunni Muslim civilians from the terrible onslaughts of the Bashar al-Assad regime in Syria, which has not hesitated to use chemical weapons in its war against its own people.
At the same time, ISIS is creating what its recruits believe to be a perfect Islamic state, trying to restore the Caliphate that ceased to exist after the end of World War I and the collapse of the Ottoman Empire.
ISIS is also even presenting itself as the vanguard of Muslim warriors who will usher in the End of Times and the final, inevitable battle between the West and Islam, which presages the arrival of the Mahdi, the savior of Islam, and the triumph of Islam over all its enemies, including the West.
ISIS also presents itself as creating a real state with plentiful social services and a place where pious young Muslim men and women from around the Islamic world can gather and even find perfect marriage partners.
For its Western recruits, there is also something glamorous and even exciting about leaving behind their humdrum lives in the West to join ISIS.
One British foreign fighter, for example, told BBC radio
: "It's actually quite fun, better than, what's that (video) game called, 'Call of Duty'? It's like that, but really, you know, 3D. You can see everything's happening in front of you, know. It's real, you know what I mean?."
What is the true level of threat?
Four years into the Syrian civil war, little evidence has emerged to support the notion that returning fighters from Syria pose a great threat to the United States. To date, there has been only one deadly attack in the West by a fighter returning from Syria: the May 24, 2014, shooting at a Jewish museum in Belgium by Mehdi Nemmouche, a 29-year-old Frenchman, that killed four people.
The threat from the 62 U.S. citizens and residents who have reportedly gone to fight in Syria and Iraq, attempted to do so, or provided support to others who have traveled to the Middle East is worrisome but far from existential, because U.S. law enforcement has generally done a good job of containing it.
Of the 62 cases, we identified only 19 individuals who actually reached Syria. Thirty-one attempted to travel to Syria but were unsuccessful, and 12 provided support to others fighting in Syria.
Far from being a launchpad for attacks at home, Syria turned out to be a graveyard for several of the Americans who traveled to fight there. Of the 19 who reached Syria, eight died there.
of Florida, for instance, died conducting a suicide bombing in northern Syria. Douglas McAuthur McCain
was killed fighting for ISIS, and a third American, Abdirahmaan Muhumed
, reportedly also died fighting with ISIS.
Given the high casualty rate in Syria, stopping Americans from a quite likely death after they are lured to Syria by predatory online ISIS recruiters may be a significant justification for focusing resources on this issue, in addition to the more obvious goal of preventing an attack in the United States by a returning fighter from Syria.