BROOKLYN--All were U.S. citizens.

They were young, unhappy, and were attracted to the ideology of the Islamic State, in part through the internet and social media.

The guilty pleas late week of two more men tied to a group of friends in New Jersey and New York who sought to join ISIS were only the latest in a series of criminal prosecutions nationwide from California to Virginia. A recent study by the Center on National Security at Fordham University School of Law found more than 100 ISIS prosecution cases filed in this country between March 2014 and June 30, 2016.

All shared much in common, said Karen Greenberg, director of the center. Nearly eight in 10 individuals charged were U.S. citizens. A third were converts to Islam. Almost 90 percent of them were young males in their 20s. And until recently, more than half were looking to find a way to get to Syria or Iraq to wage jihad.

But the nature of the terror threat to this country is apparently changing. Experts say the number of ISIS prosecutions are on the decline, as is the alleged interest in joining the ranks of foreign fighters in Syria.

"The new propaganda from ISIS is to do something where you are," said Greenberg.

Last year, only 6 out of 16 cases prosecuted last year included allegations of wanting to fight abroad for ISIS. Instead, the focus has changed into acts of violence here, said Greenberg and others, noting the arrest of Ahmad Khan Rahimi of Elizabeth, who was charged with bombings in Manhattan and New Jersey. Federal prosecutors said the 28-year-old Afghan-born naturalized citizen was inspired by international terror groups, including al-Qaida.

"The threat has evolved," agreed John D. Cohen, a professor at the Rutgers School of Criminal Justice in Newark and a senior advisor at the Rutgers University Institute for Emergency Preparedness and Homeland Security and a former intelligence official at the U.S. Department of Homeland Security. "There are fewer seeking to travel to a conflict zone. And fewer in active communications. But there seems to be more who are willing to conduct attacks on behalf of some destructive ideology--and seeing some success."

Cohen said not only are there fewer individuals seeking to go to conflict zones. The number of those in active communications with recruiters or facilitators for ISIS and other terror groups, usually through social media, is also on the decline.

"The most significant terrorism threat facing the U.S. today comes from people who are here, but are independent of any terrorist group," Cohen said.

He suggested the reasons for the shift include the changing fortunes of ISIS in Syria, as well as increased security in this country. Cohen said the U.S. has been more assertive in taking the fight overseas, with military action against ISIS serving as a disincentive. At the same time, he said U.S. Customs and Border Protection has become more sophisticated in detecting suspicious travel patterns, and scrutiny is now heavier.

ISIS, too, has changed the way it seeks to influence people, refocusing its social media in appealing to disaffected people and those seeking a cause to convince them to launch attacks right here, without the use of complicated plots.

"They are saying you can be part of this cause. You don't even have to build a bomb," Cohen said.

They can get in a car or truck and drive into a crowd, or get a gun and start shooting.

"It's very powerful. That why more people are gravitating and committing these attacks," he said.

In the case of Rahimi, accused of planting bombs in Seaside Park, Elizabeth and Manhattan, investigators found a bloodied notebook after Rahami was captured following a shootout in Linden. It contained references to Nidal Hasan, the former Army officer who gunned down 13 people at Fort Hood in 2009, and Anwar al-Awlaki, an American-born imam whose anti-Western preaching has inspired similar attacks around the world.

The capture of Ahmad Khan Rahimi, the New Jersey man accused of setting off a bomb in Manhattan that injured more than 30 people. (Ed Murray | NJ Advance Media for NJ.com)

Cohen said in an era of Rahimi and Omar Mateem, the man who opened fire at a Florida nightclub and killed 49 people last June--both cases in which the FBI received prior warnings about the threats they represented--there needs to be a change in how homegrown terrorism is investigated.

"They need a broader set of tools," he said, pointing to the Secret Service and its use of behavioral risk assessments in dealing with possible risks to the president.

Many of the ISIS cases in this country involve those who have expressed some form of social alienation, loneliness or identity issues, said Greenberg. A common denominator, she said, is a lack of finding a place in the world.

"You are dealing across ethnicity and religion and national background with those who feel excluded," she said. "Belonging to something and serving a cause has taken root."

In the case that played out in federal court last week, Munther Omar Saleh, a former student at an aeronautical engineering college in Queens, and Fareed Mumuni, 22, of Staten Island, admitted to attempting to provide material support to ISIS, and conspiring to assault federal officers.

The two were among a group of six friends in New Jersey and New York who talked about traveling to Syria to join the Islamic State. All were U.S. citizens, authorities said.

Among them was Samuel Topaz, who was born here, grew up in Fort Lee and was a talented singer with hopes of studying at a prestigious Boston music school. The investigation into the group began when his mother expressed fears to authorities in New Jersey that his friends were pushing him to "do something stupid."

He pleaded guilty in September 2015 to conspiring with others to provide services and personnel to ISIS, or ISIL as it is also known. He awaits sentencing.

His friends included classmate Nader Saadeh. According to court filings, Saadeh and Munther Saleh, were "trying to recruit" Sam by "preying on his insecurities and pain." According to prosecutors, it was Saadeh who sought first to get to Syria after learning that the deli where he worked was to be sold. He made it to Amman, where he was taken into custody by Jordanian intelligence officials and ultimately returned to the United States. He, too, pleaded guilty and is awaiting sentencing.

Saadeh's older brother, Alaa Saadeh, admitted he conspired to provide material support to the Islamic State by helping Nader fly to the Middle East. Unswayed by his statement that he now rejects the ideology of the terrorist organization, a federal judge last May sentenced him to the harshest punishment she could give him. U.S. District Judge Susan D. Wigenton imposed a 15-year term in federal prison, followed by a lifetime of supervised release. 

In Brooklyn federal court on Thursday and Friday, Munther Saleh and Fareed Mumuni entered guilty pleas as well after a series of court filings over the past year by attorneys for Saleh. They fought to suppress evidence collected under the Foreign Intelligence Surveillance Act, saying there was nothing to show he had been acting on behalf of a foreign power. Both were said to be discussing plans to build pressure cooker bombers similar to the devices used in the Boston Marathon bombing.

Prosecutors said the two were looking to commit an attack in the name of the Islamic State targeting Times Square, the World Trade Center and the Vaughn College of Aeronautics and Technology in Queens, where Saleh was then a student.

That plot never materialized.

Ted Sherman may be reached at tsherman@njadvancemedia.com. Follow him on Twitter @TedShermanSL. Find NJ.com on Facebook.

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