For months, as one young person after another in Minneapolis’s Somali community tried to join the Islamic State terrorist group, rumors circulated of a sinister terrorist recruiter who must be luring gullible teenagers and providing the cash to buy air tickets to Syria.
But on Monday, federal officials, announcing their biggest Islamic State recruitment case to date, said there was, in fact, no recruiting mastermind. Instead, for the six men arrested, there was just the camaraderie of sharing an illicit ideology, plus advice and inspiration by phone and Internet from one of their friends, a young Minneapolis man who joined the Islamic State last year.
In other words, said Andrew M. Luger, the United States attorney for Minnesota, the circle of friends “recruited each other.” He said they scrounged the money for tickets, selling a car and emptying a financial aid account, and brainstormed about how to evade the F.B.I.and reach the brutal terrorists they idolized.
The F.B.I. is increasingly concerned about this model of radicalization by peers. Because discussions of the Islamic State took place during pickup basketball games and visits to the mall, the wave of recruitment was difficult for the authorities to detect in advance. It is also a source of distress to parents in the Somali-American community, local activists say, providing no nearby villains to blame for leading their children astray.
The head of the Minnesota F.B.I. office, Richard T. Thornton, said crucial help in stopping the recruits came from inside the Somali community, including a young man who changed his mind about the Islamic State, also called ISIS or ISIL, and became an informant in January.
“These courageous men and women,” Mr. Thornton said of the local Somalis, “decided to do something to prevent more Minnesotans from traveling and dying in support of a terrorist organization which is evil to its core.”
All of those charged were Somali-Americans ages 19 to 21 from Minneapolis, where four were arrested on Sunday. The other two were detained in San Diego, where officials said they had driven to buy fake passports, hoping to cross into Mexico and continue to Syria from there.
A linchpin in the recruitment effort, it turned out, was Abdi Nur, 21, who left Minneapolis last May and successfully reached Syria. Mr. Nur, whose story was recounted by The New York Times last month, has become “an active recruiter” who offered encouragement and practical tips to those who wanted to follow his path, Mr. Luger said at a news conference.
During a 10-month investigation, the F.B.I. struggled to discover how the Islamic State was luring Minnesotans. Speculation surrounded a local man, Amir Meshal, 31, who had been expelled from two mosques and publicly accused of radicalizing young Muslims. But Mr. Meshal, who had vehemently denied supporting the terrorist group, was not charged.
Instead, Mr. Luger said, the recruitment was “a peer-to-peer operation” in which friends compared notes on how to raise money for plane tickets and connect with Islamic State travel facilitators in Turkey.
Arrested in Minneapolis were Zacharia Yusuf Abdurahman, 19; Adnan Farah, 19; Hanad Mustafe Musse, 19; and Guled Ali Omar, 20. The two men arrested in San Diego were identified as Abdirahman Yasin Daud, 21, and Mohamed Abdihamid Farah, 21, Adnan Farah’s brother. All were charged with conspiring to provide material support to a designated terrorist organization.
Mr. Daud and Mohamed Farah had driven to San Diego in Mr. Daud’s car accompanied by the friend who had become an informant. The informant, who was not named in court documents, had claimed he could get them forged passports to enter Mexico.
In November, in an earlier bid to leave the United States, Mr. Abdurahman, Mr. Musse and Mohamed Farah traveled by bus to Kennedy Airport in New York but were prevented from boarding. Their companion, Hamza Ahmed, 19, was removed from a plane minutes after boarding and subsequently charged.
But even after that encounter with the authorities, Mr. Luger said, “they never stopped plotting to find a way to get to Syria to join ISIL.” Others in the group were confronted by their parents and blocked from leaving, but decided to try again.
The court documents disclose that another Minneapolis man, referred to as “Y.J.,” evaded the F.B.I., flew to Turkey in June and called his family from the same telephone number used previously by Mr. Nur after he arrived in Turkey. He appears to have reached the Islamic State.
Those arrested on Sunday are among just a few dozen Americans who have traveled or tried to travel to Syria to join the Islamic State. Those whose plans were discovered by the F.B.I. have been arrested, usually at an American airport as they tried to board a flight.
Those intercepted have been a diverse group, including many women, with ages ranging from the early teens to late 40s, and comprising both converts to Islam and children from Muslim immigrant families.
The largest single group, however, has consisted of Somali-Americans from Minnesota, a community that experienced a previous wave of young men departing to fight with the Shabab, the Qaeda affiliate in Somalia. Mr. Omar’s older brother, in fact, has been charged with joining the Shabab in 2007 and remains a fugitive.
The F.B.I. has been intensively investigating how the Islamic State’s recruiting has worked, and whether the sophisticated social media campaign of the terrorist group is supplemented by face-to-face recruiting in the United States. The answer on Monday seemed to be that like gang members or corner drug dealers, the recruiting relied largely on friendship networks and the thrill of a dangerous mission.
Members of the group did not hide their admiration for the Islamic State’s ideology. On his Facebook page, Adnan Farah featured a picture of Anwar al-Awlaki, the Yemeni-American cleric who joined Al Qaeda in Yemen and was killed in a drone strike, the charging papers said. Since moving to Syria, Mr. Nur has periodically posted online photos and messages about his life with the Islamic State on Twitter, Ask.fm and other sites.
Even as Mr. Nur has tried to recruit others, the friend with whom he plotted his getaway has had a very different fate. Abdullahi Yusuf, then 18, was prevented from boarding his flight. Since then, Mr. Yusuf has pleaded guilty and is living in a halfway house under close supervision, while advocates work closely with him in what is seen as a national test case for deradicalization.
The number of Islamic State recruits from the United States remains small in comparison with Western Europe, where more than 3,000 people are believed to have traveled to Syria to join the group. But law enforcement and intelligence officials have tried to disrupt the travel in part because they were concerned that Americans could train with the Islamic State and then return to the United States to carry out attacks.
In the first case of its kind, a 23-year-old Somali-American from Columbus, Ohio, was charged last week with training in Syria — whether with the Islamic State or another group was left unclear — and being directed by a cleric there to go home to the United States and carry out an attack.
The authorities said the man, Abdirahman Sheik Mohamud, a naturalized American citizen whose brother was killed last year fighting in Syria with another militant group, the Nusra Front, spoke of wanting to attack a military base. He mounted no attack, however, and was arrested in February.
