"In response to the terrorist acts of September 11, 2001, Congress passed legislation making permanent a provision that allows aliens with critical information on criminal or terrorist organizations to come into the United States to provide information to law enforcement officials. This legislation (S. 1424) became P.L. 107-45 on October 1, 2001. The law amended the Immigration and Nationality Act to provide permanent authority for the administration of the 'S' visa, which was scheduled to expire on September 13, 2001. On November 29, 2001, then-Attorney General John Ashcroft announced the 'Responsible Cooperators Program' to reach out to persons who may be eligible for the S visa. Up to 200 criminal informants and 50 terrorist informants may be admitted annually. Since FY1995, more than 500 informants and their accompanying family members have entered on S visas. No terrorist informants have been admitted into the U.S. since 1996."
CRS Report for Congress, RS21043