An Islamic State fighter walks near a black flag belonging to the Islamic State as a Turkish army vehicle takes position near the Syrian town of Kobani on Oct. 7, 2014. Reuters

An online predator was behind the case of the three teenage girls who left Colorado to join the Islamic State group, also known as ISIS, an official told the Associated Press. The girls -- a 16-year-old and two sisters, 17 and 15 -- are back home in Denver after the FBI found them in Frankfurt, Germany, on their way to Syria.

Someone communicated with at least one of the girls online, Cherry Creek School District spokeswoman Tustin Amole told the AP. The person encouraged them to come to Syria. They may have been swayed by “promises of husbands and homes,” which extremists have used to gain supporters on social media, according to the AP. ISIS’ Internet presence is strong, and the militants often use it for recruitment. "There's no indication they had been radicalized in a way that they wanted to fight for ISIS," Amole said.

The Atlantic reported the girls’ parents think ISIS contacted them directly. The 17-year-old spent months organizing the trip and involved the other two. None of the American girls, two with a Somalian background, one with Sudanese, had ever run away, CNN reported. “These are good girls,” Amole told NPR. “We've never had a history of issues with them. We've never seen indication of any propensity for violence.”

They looked at extremist websites to find out how to travel to Syria, but their searches didn’t trigger any FBI mechanisms used to find potential jihadists, CNN reported. They even discussed their travel plans on Twitter.

Since being home, the FBI has been in touch with the girls. A U.S. official told the AP that investigators were reviewing the teens’ computers. The girls admitted to stealing $2,000 and their passports from their parents, according to the offense report. But when an Arapahoe County Sheriff’s Office deputy asked why they went to Germany, they said, “family” and wouldn’t explain further.

It’s unclear whether the girls will be federally charged. The state and school district told the AP that they didn’t have plans to discipline them.