I haven't read the decision yet, but it appears the Court struck down the measures of the law that made it a crime for an illegal immigrant to be in or apply for work in the State of Arizona, and the provision that allowed State law enforcement to make warrantless arrests and detentions of individuals that they believe are illegal aliens. I think this ruling was expected on the basis of federal preemption.

The "papers please" provision that makes it mandatory for the police to detain anyone arrested for anything until the officer can ascertain the immigration status from the federal authorities. Nothing before this Act prevented an arresting officer from checking with Immigration. The Act, as I understand it, removes discretion and requires everyone to be checked, which, of course won't be done.

Not having read the decision, I understand that the remand to the Ninth Cir. is to determine whether that narrow issue is supplanting or supporting federal law. I'm a bit surprised though that none of the Justices determined that from the given facts. One way or another, we haven't heard the last of this remaining issue.