Authorities believe that several pro-ISIS documents and a letter written by the Illinois teen arrested for trying to join the Daesh terrorist cell proves his intent on joining the international terrorist group.

Nineteen-year-old Mohammed Hamzah Khan was taken into custody and charged with a terrorism-related offense after he allegedly tried to join the Islamic State of Iraq and Syria (ISIS) on October 4.

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According to prosecutors, Federal Bureau of Investigation agents found documents, including a round-trip plane ticket from Chicago to Istanbul and a letter he reportedly wrote indicating the American citizen's intention to join the international terrorist group.

According to reports, Khan had contacted a person over the Internet who promised to guide him to ISIS strongholds in Iraq and Syria after he arrived in Istanbul.

The three-page letter, addressed to his parents, cited how he condemns Western society because of its immorality.

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

Before warning his parents not to tell authorities about his plan, he extended to them an invitation to join the international terror group and described them as "lions of war."

According to a CNN report, Khan waived his Miranda rights and told the officers who apprehended him that he planned to fight alongside ISIS in Turkey.

The teen from Bolingbrook, Illinois was apprehended at O'Hare International Airport after he left a trail of evidence leading authorities to his whereabouts just before he boarded the plane to Turkey.

Prosecutors believe they can prove his guilt by using the letter as the strongest evidence against the 19-year-old terrorist wannabe.

If convicted, Khan is faced with a maximum of 15 years in prison and a $250,000 fine.

TagsUS, Chicago, Illinois, teen, ISIS, Daesh, ISIL, Terrorist, western, Turkey, Iraq