A 19-year-old from the Chicago suburb of Bolingbrook was arrested on Saturday at O’Hare International Airport and charged with attempting to provide material support to ISIS. Authorities say Mohmmed Hamzah Khan planned to fly to Turkey to meet an ISIS contact who was to take him into Syria.

Prosecutors haven’t said how they knew about Khan’s plans, but he’s reportedly admitted since his arrest that he intended to join the terrorist group. An alleged letter to his parents found during a search of the Khan family’s home also bodes ill for his potential defense. From USA Today:

“FIRST and FOREMOST, PLEASE MAKE SURE TO NOT TELL THE AUTHORITIES For if this were to happen it will jeopardize not only the safety of us but our family as well,” the letter addressed to Khan’s parents said…Khan invited his family “to join me in the Islamic State.”

The charges against Khan are punishable by up to 15 years in prison.

