After the attacks of September 11 , 2001 , the United States government announced a campaign of aggressive detention , by whatever means possible , of those potentially involved in attacks on the United States . The means included using the material witness statute to detain even suspects ( as opposed to witnesses ) . Many of those detained as material witnesses were detained as witnesses to grand jury proceedings , which only investigate and are not criminal trials
attacks of September 11 , 2001
September 11 attacks
Material witness