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(CNN) —  

Despite its losses on the battlefield in Iraq and Syria, the Islamic State remains a grave national security threat, according to the Trump administration and terrorism experts.

That mixed news was brought home just last week. Last Wednesday, the Department of Homeland Security extended its warning of homegrown terror threats to the US for the fifth time since December 2015. That was followed on Thursday by a tweet from President Donald Trump touting the reported capture of five top Islamic State commanders in Iraq. Over the weekend, ISIS claimed responsibility for a knife attack in Paris that left one dead and four injured. The perpetrator was killed by police.

FBI Director Christopher Wray described the changing dynamics of the ISIS threat on Capitol Hill in December.

“The good news is the caliphate is crumbling, and that’s positive for all of us,” Wray said during a House Judiciary Committee oversight hearing. “The bad news is, ISIS is encouraging some of its recruits and potential recruits to stay where they are and commit attacks right in the homeland.”

FBI Director Christopher Wray seen here on Capitol Hill in February.
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FBI Director Christopher Wray seen here on Capitol Hill in February.

Wray said agents are tracking would-be lone wolf Islamic State terrorists en masse, with about 1,000 active ISIS investigations spread across all 50 states. But while the FBI may be pursuing hundreds of ISIS cases, it hasn’t been prosecuting radical Islamic extremists at a steady clip this year.

The total number of publicly revealed ISIS indictments or guilty pleas in 2018: four.

The total number of publicly revealed ISIS arrests in 2018: one.

A CNN analysis of court documents and government news releases shows a dramatic drop in ISIS prosecutions in 2018, the longest stretch of quiet since the government designated the Islamic State as a foreign terrorist organization four years ago. CNN reviewed Justice Department news releases and searched federal court records for criminal cases involving material support of a foreign terrorist group.

The Justice Department and the FBI declined to answer a list of detailed questions about ISIS arrests and investigations, instructing CNN to submit a request through the Freedom of Information Act.

Steady decline in prosecutions since 2015 peak

The peak year for ISIS prosecutions in the US was 2015, when 57 people were charged with material support or related offenses. Wannabe travelers got apprehended at airports before boarding international flights and domestic plots were foiled by FBI stings. In 2016, the number of prosecutions fell to 34. The decline continued in 2017, with 26 indictments or pleas in ISIS cases.

It’s possible that there have been more than four ISIS prosecutions and one arrest in 2018, but the information isn’t available to the public.

The FBI doesn’t announce the arrest of a terror suspect if agents are still investigating co-conspirators. Court documents often remain sealed until all of the participants in a plot are taken into custody, said Barbara McQuade, a law professor at the University of Michigan and former US attorney.

For instance, in May 2016 a Canadian man named Abdulrahman El Bahnasawy was arrested in New Jersey for plotting a New York City subway bombing and a mass shooting at a concert venue. His indictment was kept under wraps for more than a year while authorities pursued two of his associates overseas. The case was unsealed in October 2017, after the associates were detained in Pakistan and the Philippines.

Several factors may be contributing to the slowdown in prosecutions. The Islamic State’s main recruiting tool, its self-declared caliphate, has been reduced to a cluster of towns in the Euphrates River Valley, according to IHS Markit, a global security research firm. Last year, ISIS was defeated in key cities including Raqqa and Mosul. The amount of propaganda released by the terror group plummeted 62% in 2017, IHS Markit reports.

“As ISIS loses that propaganda machine, fewer people are going to be radicalized by it because fewer people are going to pay attention to it,” said Jeffrey Ringel, a former FBI special agent and director of the Soufan Group, a security consulting firm.

The ISIS threat still looms, however. Four days after Wray appeared on Capitol Hill last December, an ISIS follower attempted to detonate a pipe bomb at the Port Authority bus terminal in New York, injuring five. Last Halloween, eight people were killed when a driver rammed a rental truck into a crowd on a Manhattan bike path, the deadliest act of terrorism in New York since 9/11.

“Currently, the FBI views ISIS and homegrown violent extremists as the main terrorism threats to the United States,” Wray said during the December oversight hearing. “ISIS is relentless and ruthless in its campaign of violence and has aggressively promoted its hateful message, attracting like-minded violent extremists.

“The threats posed by ISIS foreign terrorist fighters, including those recruited from the US, are extremely dynamic. These threats remain the highest priority and create the most serious challenges for the FBI, the US intelligence community, and our foreign, state, and local partners.”

Given Wray’s testimony that the agency had about 1,000 active ISIS investigations at the end of last year, the dearth of cases in 2018 is noteworthy, according to five terrorism experts.

“It’s surprising,” said Karen Greenberg, director of the Center on National Security at Fordham University School of Law. “The question is what does it mean? Does it mean the war on terror has moved beyond ISIS? I think the public is confused. The public is asking, ‘Where exactly do we stand?’

“The good news is that maybe the threat is less and that’s what we’re learning. The bad news: Is the threat less or are we handling it in other ways? We only know what the government decides to tell us.”

Ringel said the downward trend in cases proves the ISIS prosecutions have been a powerful deterrent. The conviction rate for ISIS-related cases is close to 100%.

“The US has been very successful in discouraging support of terrorist groups because people realize they’re gonna get caught,” said Ringel.

There’s another way to look at it, according to Michael German, a former FBI special agent and a fellow at the Brennan Center for Justice’s Liberty and National Security Program.

“If you have a thousand investigations of any group and only a handful of prosecutions, it proves that those investigations aren’t properly predicated,” said German.

Seamus Hughes, deputy director of the Program on Extremism at George Washington University, said fewer people are being charged because the investigations are growing more complicated.

“If you look back at the cases, a good majority of them were individuals who got arrested attempting to go to Syria and Iraq, which are easier cases to make because if somebody drives to the airport, that’s the trigger for the charge of material support of terrorism,” said Hughes. “If you don’t have that, it’s going to take longer to build a case.”

Social media behind increase in investigations

The number of counterterrorism investigations has increased over the past decade, in part because technology provides law enforcement with leads, said Daniel Byman, a senior fellow at the Center for Middle East Policy at the Brookings Institution. Social media enables the FBI to locate suspects. Court records show that many ISIS probes begin with a review of Facebook profiles and Twitter feeds.

It takes time and resources for the FBI to weed through ominous internet posts and determine whether an individual is bloviating for shock value or if they’re making true threats that need to be chased down, said Byman.

“You have a lot of people bragging on social media and that comes to the attention of authorities,” said Byman. “Ten years ago, that same person might have been bragging to their friends in their bedroom and they wouldn’t have come to the attention of authorities. In most cases, it never would have gone further than three guys bragging in their bedroom about how badass they are.

“But occasionally, it does. The FBI’s point of view would be, ‘Yeah, most of the time it doesn’t lead to much but sometimes it does, and we don’t want any people to die because we didn’t take someone who said, “I want to kill people” seriously.’ ”

Recent ISIS-related arrests in the US

Akayed Ullah, 27, the man who injured himself wearing a clumsily assembled suicide vest containing a pipe bomb at the Port Authority in December, was indicted on January 10. The six counts include material support and use of a weapon of mass destruction. He’s pleaded not guilty.

The other three 2018 ISIS prosecutions involve allegations of domestic terror plots.

Everitt Aaron Jameson, 26, of California, was charged in January after a three-month sting operation with two undercover agents and a paid informant. According to court records, Jameson discussed a Christmas season attack on a popular shopping area in San Francisco but he ultimately backed out, telling an undercover agent, “I also don’t think I can do this after all. I’ve reconsidered.”

Although Jameson bailed on the attack, he was arrested after the FBI executed a search warrant and interviewed him. At his home, agents found guns, empty magazines, a letter lauding ISIS leader Abu Bakr al-Baghdadi and Jameson’s last will and testament. Jameson told the agents, according to court documents, that he supported ISIS and would be “happy” if someone else committed an act of domestic terrorism. He was charged with attempted material support and distribution of information related to destructive devices. He initially pleaded not guilty but a change of plea hearing is scheduled for June 4.

Aziz Ihab Sayyed, 23, of Alabama, pleaded guilty in March to attempted material support, admitting that he had purchased bomb-making materials and planned to plant explosive devices at police stations and a military base. His sentencing is set for June 20.

Gregory Lepsky, 20, of New Jersey, was arrested in 2017 after he stabbed his dog with a combat knife and cut his arm. As detailed in a criminal complaint, he said the animal was “dirty” according to his interpretation of Islam.

While in police custody, he told medical personnel that he was communicating with ISIS members on Facebook and he wanted to set off a pressure cooker bomb in New York City. Searches of his computer and phone revealed Islamic State propaganda, anti-Semitic cartoons, photos of Lepsky holding guns and an al Qaeda magazine article titled “How to Build a Bomb in the Kitchen of Your Mom.” A pressure cooker was found in his bedroom closet. After a psychiatric evaluation was submitted to the court, Lepsky pleaded guilty in March to attempted material support.

The one ISIS arrest for 2018 involved an American suspect who was extradited to the US. Bernard Augustine, 21, of California, returned from Tunisia in February and was charged in a criminal complaint with attempted material support. Augustine, who traveled overseas in 2016, allegedly intended to join ISIS in Libya. He was sent back to the United States after serving more than a year in a Tunisian prison. Augustine has not yet been indicted and is engaged in plea negotiations, according to a spokesman for the US Attorney’s Office for the Eastern District of New York.

In an unusual case, a Virginia man who was under investigation for possible ISIS support pleaded guilty to receipt of child pornography after investigators found thousands of images on his phone, including pictures of infants being sexually abused. Sean Andrew Duncan, 22, admitted last month that he had received child pornography and obstructed justice but he was not charged with material support. Sentencing is set for July 6.

There was also one high-profile arrest of a juvenile. The FBI participated in the investigation of a Texas high school student, Matin Azizi-Yarand, 17, who told two informants and an undercover agent that he wanted to carry out a mass shooting at a suburban mall in the name of ISIS. Azizi-Yarand was arrested on May 1 and is being held at the local county jail. Calls to his attorneys were not returned.

Because he is a juvenile under federal law, Azizi-Yarand will not be prosecuted by the US Justice Department, according to US Attorney Joseph D. Brown. Instead, the local district attorney’s office has charged him with solicitation of capital murder and making a terroristic threat. In the Texas criminal justice system, he can be tried as an adult.

The Azizi-Yarand case illustrates how individuals can have mixed motives. Although the teen frequently praised ISIS, he also discussed the Columbine and Parkland school shootings, according to court documents.

“There are going to be individuals who want to commit violent acts and then they talk about ISIS when they do so, and you have to look at that with a grain of salt,” said Hughes, of George Washington University.