Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Before authorities arrested him at O'Hare International Airport and accused him of attempting to provide aid to ISIS, a teen from the Chicago suburbs left behind a letter for his parents. Mohammed Hamzah Khan, 19, wrote that he was leaving the United States and on the way to join ISIS, according to a criminal complaint. He invited his family to join him in the three-page letter, which authorities found in the bedroom he shared with a sibling in Bolingbrook, Illinois. But he warned them not to tell anyone about his travel plans, the complaint said. "First and foremost, please make sure not to to tell the authorities," he wrote, according to the complaint. "For if this were to happen it will jeopardize not only the safety of us but our family as well."Congressman: "There are other Americans who are being recruited" by ISISMohammed Hamzah Khan made his first court appearanceThe 19-year-old was arrested at O'Hare International Airport on SaturdayAuthorities allege there is evidence that he wanted to join ISIS 
 Question:The search at Khan's Bolingbrook home, where he lives with his parents, turned up documents allegedly written by _ that stated his intentions.

Mohammed Hamzah Khan