Consular Notification and Access: Instructions for Federal, State, and Local Law Enforcement and Other Officials Regarding Foreign Nationals in the United States and the Rights of Consular Officials to Assist Them [open pdf - 4MB]
"This booklet contains instructions and guidance relating to the arrest and detention of foreign nationals, the appointment of guardians for minors or incompetent adults who are foreign nationals, and related issues pertaining to the provision of consular services to foreign nationals in the United States. This booklet is designed to help ensure that foreign governments can extend appropriate consular services to their nationals in the United States and that the United States complies with its legal obligations to such governments. The instructions and guidance herein should be followed by all federal, state, and local government officials, whether law enforcement, judicial, or other, insofar as they pertain to foreign nationals subject to such officials' authority or to matter within such officials' competence."
U.S. Department of State Bureay of Consular Affairs: http://travel.state.gov/