The American Civil Liberties Union filed legal papers urging that a former Chicago gang member accused of plotting with terrorists to detonate a radioactive dirty bomb be tried in court.

In papers filed Thursday in U.S. District Court, the civil liberties organization said "precedent and principle" require that Jose Padilla be tried in court, with a lawyer representing him, rather than held indefinitely as an "enemy combatant."

"The higher the stakes, the more important it is to ensure that the government does not act arbitrarily or in error," the ACLU wrote.

Padilla, 31, was arrested May 8 and secretly held in a federal jail on a material witness warrant issued by a New York grand jury. The government said Padilla twice met with senior Al Qaeda operatives in Karachi, Pakistan, in March and discussed a plot to detonate a radiological weapon in the United States.

On June 9, President Bush decided that Padilla was an enemy combatant and should be transferred to the control of the U.S. military. He was flown the next day to a Navy brig in Charleston, S.C.

Padilla's lawyer, Donna Newman, has argued in court that he is being held illegally and should be released.