Be it noted that Chief of Police Beck of LA is- well,

let's let Dunphy say it:

Beck said that his officers are guided by a different set of rules than the ones laid out in the Arizona law. For more than three decades the LAPD has followed a policy that prohibits officers from initiating contact with someone solely to determine whether he or she is in the country legally.

Assuming the L.A. Times has accurately paraphrased Beck’s statement, we can reach either of two possible conclusions: that he is misinformed on the language of the new law, or he is deliberately distorting the truth to serve a political agenda. Neither choice is comforting.
(isn't that a nice way to say Beck's either a fool or a liar?)

Like the LAPD policy in place since 1979, the Arizona law specifically prohibits officers from stopping anyone for the sole purpose of determining his immigration status. Arizona goes beyond the limits of the LAPD policy only in that it allows inquiry into an individual’s immigration status after a detention based on reasonable suspicion rather than an arrest based on probable cause. The reasonable suspicion must concern some crime other than illegal immigration. This important provision has been widely reported but just as widely ignored by those who seek to discredit the new law and forestall its enforcement.