CHICAGO (CBS) — A Bolingbrook man’s younger brother and younger sister were arrested with him last month when they allegedly went to O’Hare International Airport to fly overseas to join the Islamic State terrorist group.

Mohammed Hamzah Khan was arrested at O’Hare on Oct. 4, as he was going through a security checkpoint before a flight to Vienna, Austria, and then to Istanbul, Turkey.

At a detention hearing Monday, federal prosecutors revealed his 17-year-old sister and 16-year-old brother also were arrested. Prosecutors did not identify the siblings, who have not been charged with a crime.

Prosecutors said the three siblings expressed a desire to commit violence, and act on “barbaric rhetoric” if they managed to sneak into Syria and join the Islamic State terrorist group, which has seized control of large swaths of Iraq and Syria.

U.S. Magistrate Judge Susan Cox ordered Khan detained pending trial, after federal prosecutors told her Khan had planned the trip for months, and purchased the plane tickets for himself and his siblings. Federal prosecutors argued he is a flight risk, and a danger to the community.

Cox had earlier denied a government request to bar the public and media from parts of Monday’s detention hearing, to protect the identities of Khan’s siblings, but Cox said she wasn’t convinced privacy concerns trumped the right to a public trial.

Khan’s defense attorney, Thomas Durkin, called the government’s case “hopelessly weak” and asked that Cox release Khan on home confinement. He said the family was willing to post their home as collateral, using $100,000 in equity.

Khan has been charged with attempting to provide material support to a foreign terrorist organization, a charge that carries a sentence of up to 15 years.

After Khan was detained at O’Hare, federal agents obtained a warrant to search his home, where they allegedly found hand-written documents there that appeared to be drafted by Khan and/or others, expressing support for the Islamic State, also known as the Islamic State of Iraq and Syria (ISIS) or the Islamic State of Iraq and the Levant (ISIL).

The notebook indicated Khan wanted to travel to Syrian border.

“We are the lions of War,” Khan wrote. “My nation, the dawn has emerged.”

The notebook also had a drawing of the Islamic State flag.