"The [material witness] statute, which authorizes such detentions under court supervision for "a reasonable period of time" in order to secure testimony, is not new. It has long been used with relatively little controversy in organized-crime cases.
But since the Oklahoma City bombing investigation and particularly since Sept. 11, 2001, designation of material witnesses has become a more routine tool in the government's legal arsenal and has been deployed at an earlier stage of criminal proceedings. Rather than being used merely to ensure that witnesses are available for trial after an indictment has been issued, it has been employed to hold suspects who are themselves under investigation. The result is that dozens of people across the country have been detained for varying periods of time while the government seeks to compile evidence against them. The circumstances of these detentions are shrouded in secrecy, as are the names of the detainees and even the raw number of them. The Justice Department at times has seemed to use the statute as a kind of preventive detention law."