WHY HAVE I BEEN DETAINED?

Immigration authorities, certain federal and state law enforcement officers and most recently local/municipal police departments are empowered to temporarily detain anyone that the officer suspect may be in the United States, illegally. That detention must be reasonable and it's duration only that sufficient to verify or dispel the officer's suspicion of illegal presence. If the officer determines that an individual is indeed in the United States without the proper and valid visa, or if the individual detained has committed a deportable offense, then the officer can incarcerate the detained alien.