Was arrested teen on his way to join ISIS?

(CNN) -- A teen from the Chicago suburbs was arrested at O'Hare International Airport over the weekend and accused of attempting to provide aid to ISIS, the U.S. attorney's office for the Northern District of Illinois announced Monday.

Mohammed Hamzah Khan, 19, is charged with one count of attempting to provide material support to a foreign terrorist organization.

According to a criminal complaint, a round-trip ticket was purchased for Khan from Chicago to Istanbul.

In an interview with FBI agents and a letter to his parents, Khan indicated that he did not plan to return and was on his way to join ISIS.

Once he crossed security at the airport Saturday, federal agents stopped him and executed a search warrant at his home, where documents expressing support for ISIS and jihadists were recovered, the U.S. attorney's office said.

The teen was taken into custody without incident.

The charge he faces carries a maximum penalty of 15 years in prison and a $250,000 fine.

Details about who purchased the airplane ticket for Khan and whom he was planning to meet in Turkey were not included in the criminal complaint.

But the court document does state that the FBI has withheld many details for now, including in the document only enough to persuade a judge to criminally charge Khan.

The search at Khan's Bolingbrook, Illinois, home, where he lives with his parents, turned up documents allegedly written by Khan that stated his intentions.

In his bedroom, he left a three-page handwritten letter telling his parents that his destination was Syria and warning them not to tell authorities about his trip because it could put his safety in jeopardy, according to the criminal complaint.

In the letter, Khan wrote that there is an obligation to "migrate" to ISIS-controlled territory.

ISIS, an extremist Islamist group, has been fighting to take over a swath of territory in Iraq and Syria where it wants to establish a caliphate or Islamic state.

"We are all witness that the Western societies are getting more immoral day by day," Khan is wrote in the letter, according to the complaint. "I do not want my kids being exposed to filth like this."

Finally, he asks his family to join him in the "Islamic State."

During questioning at the airport, Khan waived his Miranda rights and told FBI agents that a person he met online (not identified by name in the court document) 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 to ISIS territory.

According to the complaint, Khan told authorities he was planning on being in some type of public service -- like a police force -- or providing humanitarian work or a combat role.

Turkey, the complaint notes, is a common transit point for foreign fighters from Western countries who travel to join ISIS.