A look at four Americans who became jihadis, and what motivated them to fight:
Moner Mohammad Abusalha, who liked to cuddle cats, blew himself up in May in Syria. He was the first American suicide bomber in that civil war.
Abusalha, 22, was a community college student who grew up playing basketball in Vero Beach, Florida. But Abusalha, the son of a Palestinian father and Italian-American mother, became increasingly consumed with religious fervor.
He said he was influenced by a close, radical friend, according to a video he made before he killed himself and 16 others while fighting with the Nusra Front, al-Qaida's branch in Syria.
Both decided that jihad was for them, but when it was time to go, the friend backed out.
Before getting to Syria, Abusalha was in Istanbul, Turkey. He describes his time there as a low point in his life.
In the video, he says he saw a cat outside a Turkish mosque. "I see this beautiful cat and I start playing with the cat. ... Even though I'm sad, I still feel happy. I see this cat and I feel happy."
Shannon Maureen Conley, 19, a nurse's aide from suburban Denver, was arrested in April as she boarded a flight at Denver International Airport. It was to be the first leg of a journey to Syria, where she wanted to fight with jihadis. She believed it as her only answer to correcting what she saw were wrongs perpetrated against the Muslim world.
The Muslim convert told FBI agents that she wanted to marry an online suitor from Tunisia who said he was fighting with the extremists. She wanted to use her American military training from the U.S. Army Explorers to fight or be a nurse at the man's camp.
FBI agents became aware of Conley's growing interest in extremism in November 2013 after she started talking about terrorism with employees of a suburban Denver church. They had seen her wandering around and taking notes on the layout of the campus, according to court documents.
Her lawyer, Robert Pepin, said she was misled while exploring her faith.
Conley pleaded guilty this month to one count of conspiracy to provide material support to a foreign terrorist organization. She is to be sentenced in January.
Mufid Elfgeeh, a 30-year-old naturalized U.S. citizen in Rochester, New York, was arrested in May after he bought two handguns and a pair of silencers that federal officials said he planned to use to kill U.S. veterans of the Iraq fighting and Shiites living in the Rochester area.
On Thursday, Elfgeeh, a Sunni Muslim who was born in Yemen, pleaded innocent to new federal charges that he tried to aid the Islamic State group. Court papers say the food mart owner tried to arrange for three individuals to travel to Syria to join the Islamic State fighters.
He said he was thinking about doing something in New York to avenge the U.S. "killing machine."
Elfgeeh told an FBI informant in December 2013: "I'm thinking ... just go buy a big automatic gun from off the street or something and a lot of bullets and just put on a (bulletproof) vest or whatever and just go around and start shooting."
He once tweeted: "al-Qaida said it loud and clear: We are fighting the American invasion and their hegemony over the earth and the people."
They both were converts to Islam, and both ended up dead on extremists' battlefields halfway around the world.
Each had tattoos on the right side of their necks, marks that helped identify them once they were killed.
Troy Kastigar, 28, went first, leaving Minneapolis in November 2008. He had become friends with another man who was getting ready to join the al-Shabab terrorist group in Somalia. A year later he was killed there while fighting African Union troops sent to back the transitional government in Somalia.
"If you guys only knew how much fun we have over here — this is the real Disneyland," Kastigar said in a 40-minute video released by al-Shabab that also showed his shrouded corpse.
His basketball buddy, Douglas McAuthur McCain, 33, of suburban Minneapolis followed him into the terrorism fight, ending up in Turkey, a frequent entry point to Syria. He was killed this year in Syria fighting with the Islamic State group.
McCain, who last lived in San Diego, once said in a Twitter feed that embracing Islam was the best thing he'd ever done. He was following Islamic State group fighters on Twitter, but it's unclear what prompted them to join the fight.