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 could n'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 did n'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 . Why is ISIS so successful at luring Westerners ? 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 . How ISIS makes its millions .
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 .