A Justice Department memo contends that al-Qaeda members in Colorado's Supermax prison coordinated a mass hunger strike in 2006 by tapping on metal pipes to communicate, according to The Washington Post . "Even those terrorists kept in physical isolation within maximum security facilities can often find ways of communicating and thereby compromising institutional security," reveals an August 31, 2006 document signed by Steven G. Bradbury, the acting assistant attorney general for the department's Office of Legal Counsel at the time. The memo, which is posted on the American Civil Liberties Union's Web site , comes as officials debate where to place detainees after the prison at Guantanamo Bay is closed, which President Barack Obama has ordered. The memo presents legal justifications for the CIA's "black site" prisons, where terrorism suspects were held outside the U.S. legal system between 2002 and 2006. It could also be used to argue that al-Qaeda members should not be allowed in U.S. prisons. Recently, Richard Reid , the would-be "shoe bomber," launched a hunger strike in apparent protest of Supermax's denial of his religious dietary requirements.