- People who know Mohammed Hamzah Khan describe him as nice and polite
- "He's the last person that we'd think that would happen to," says a member of his mosque
- Khan lives in Bolingbrook, a working-class suburb of Chicago, with his family
- He graduated from an Islamic school on his street and taught at a local mosque, neighbors say
The arrest of an American teenager for allegedly attempting to join the Islamic militant group ISIS has stunned people in the working-class Chicago suburb where he lives.
Neighbors and attendees of a local mosque described Mohammed Hamzah Khan, 19, as a nice, polite young man.
"He's the last person that we'd think that would happen to," Bahauddin Ali Khan, a member of the mosque that Khan regularly attended in Bolingbrook, Illinois, told CNN affiliate WLS.
FBI counterterrorism agents arrested Khan on Saturday at O'Hare International Airport where he was planning to fly to Vienna and then onward to Istanbul, according to the U.S. Department of Justice.
Letter to family
He had reportedly explained his reasons for attempting the journey in a three-page letter he left for his family in the bedroom he shared with a sibling in Bolingbrook.
He invited his family to join him in the "Islamic State" -- the name ISIS uses to refer to itself -- but warned them not to tell anyone about his travel plans, according to a criminal complaint.
Khan wrote that there is an obligation to "migrate" to territory controlled by ISIS, which has used bloodthirsty tactics to seize control of large areas of Syria and Iraq.
"We are all witness that the Western societies are getting more immoral day by day," Khan wrote in the letter, according to the complaint. "I do not want my kids being exposed to filth like this."
He said he couldn't bear the thought of his taxes in the United States, which along with other countries is carrying out airstrikes against ISIS, being used to kill his "Muslim brothers and sisters."
Planned to meet contact in Istanbul
During questioning at the airport, Khan waived his Miranda rights and told FBI agents that a person he met online had given him the phone number of a person to call once he arrived in Istanbul.
That person, Khan told agents, was to take him into ISIS territory.
The Department of Justice said the $4,000 round-trip ticket to Istanbul was bought on September 26. But details on who purchased it for Khan and who he was to meet in Turkey were not disclosed.
According to the complaint, Khan told authorities he was planning on working in some type of public service for ISIS -- like a police force -- providing humanitarian work or taking up a combat role.
Turkey, the complaint notes, is a common transit point for foreign fighters from Western countries who travel to join ISIS.
'The kid was polite'
Khan's family members, who attended his initial appearance in a federal court Monday, have declined to talk about him, asking for privacy.
But neighbors in Bolingbrook expressed shock at the news.
"Surprised, really surprised," said Steve Moore, who says he's known the family for about two years. "The kid was polite. I didn't expect anything like that in the least bit."
Neighbors told WLS that Khan graduated from the Furqaan Academy, an Islamic school across the street from his house.
The Muslim Association of Bolingbrook, which runs the mosque Khan attended, said it will cooperate fully with authorities, the broadcaster reported.
Another of the mosque's members said Khan taught there.
"He would never get angry. Really nice guy," Ali Idrees told WLS.
Search finds writings and drawings
What's unclear is how the teenager was radicalized and if his family knew what he was planning.
Agents searched Khan's Bolingbrook home, where he lives with his family, finding pro-ISIS writings and drawings in common areas of the house, according to the criminal complaint.
That suggests some of his views may have been known to members of his family.
Khan has been charged with one count of attempting to provide material support to a foreign terrorist organization, which carries a maximum penalty of 15 years in prison and a $250,000 fine.