U.S. District Judge Murray Snow has issued rulings against Arpaio earlier in the case.
In December, he barred Arpaio's deputies who are enforcing Arizona's 2005 immigrant smuggling law from detaining people based solely on the suspicion that they're in the country illegally. Arpaio has appealed that decision.
The judge also has reminded plaintiffs' attorneys what they need to prove to make their claim of systematic discrimination. At a March hearing, he told them that to back up the racial profiling allegations, they must show Arpaio's office had a policy that was intentionally discriminatory.
The plaintiffs' attorneys say they plan to do so, in part, by focusing on their allegation that Arpaio launched some patrols based on racially charged citizen complaints that alleged no actual crimes.
Separate from the two lawsuits that allege racial profiling, a federal grand jury has been investigating Arpaio's office on criminal abuse-of-power allegations since at least December 2009 and is examining the investigative work of the sheriff's anti-public corruption squad.
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