Al-Shabab means "The Youth" in Arabic. The group uses a mixture of religion, nationalism and deception to lure young people, said Omar Jamal, a longtime local activist who now serves as the first secretary for the Somali mission to the United Nations.
"They misinform people, and they target young, impressionable kids," Jamal said. "They literally brainwash them. It's a very dangerous cult."
Al-Shabab's local recruitment efforts began in 2007 when small groups began discussing returning home to fight Ethiopian troops who entered Somalia to prop up a weak U.N.-backed government and were seen by many Somalis as foreign invaders. The recruiters aimed their appeal at the young men's patriotic and religious ideals.
Ethiopian troops pulled out of Somalia in 2009, but al-Shabab kept up its fight for power. According to Valentina Soria, a security analyst with London-based IHS Jane's, al-Shabab has increasingly focused in the past three years on the recruitment of western nationals and members of the Somali diaspora in the U.S. and Europe to offset its declining domestic support.
Anders Folk was an assistant U.S. attorney in Minneapolis for several years of the recruiting investigation before leaving for private practice. Al-Shabab's recruiting was at least as effective after the Ethiopians left as before, he said.
"Al Shabab's recruiting technique was essentially a call to jihad, that this is a religious duty," Folk said. "It was a call to jihad to come and fight."
Internet videos are a major tool for the group. Many feature scenes of men with covered faces firing automatic weapons, marching or practicing martial arts, as well as images of dead bodies and religious documents. Some show English-speaking suicide bombers reciting last wills.
The group often appeals to young men who've had trouble assimilating into American life, perhaps because they are unable to get a job, dropped out of school or got involved in gangs, Jamal said.