Though Not Linked to Terrorism, Many Detainees Cannot Go Home
In the past, visa violators who had no other charges against them were usually deported or allowed to leave voluntarily 60 to 90 days after their immigration cases were closed, lawyers said. But these detainees are being treated differently.

American officials acknowledged a great reluctance to release people who could be involved with terrorism and said that the Federal Bureau of Investigation was working hard to complete the checks.

"We have to be very careful about the people we let go," said a senior Justice Department official, who spoke on condition of not being identified by name.

Civil liberties advocates agreed that the government needed to be careful but said the delays were stretching the normal legal timetables. The government, they said, was in the dubious position of holding people indefinitely without charging them with a crime.
http://www.nytimes.com/2002/02/18/national/18DETA.html?todaysheadlines&pagewanted=all