U.S. District Judge Murray Snow hasn't yet ruled on the ultimate question of racial profiling, but notes the case's evidence could lead a judge or jury to conclude that Arpaio's office racially profiles Latinos.
"Sheriff Arpaio has made public statements that a fact-finder could interpret as endorsing racial profiling," Snow said.
The judge noted that the sheriff has said that even without authority to enforce federal immigration laws, his officers can detain people based upon their speech or they appear to be from another country.
The 40-page ruling marked a qualified victory for the lawyers who pushed the lawsuit. They didn't get the case decided without going to trial, as they had hoped, but it came closer to the result they were looking for.
"We are encouraged by the Court's recognition of the strong evidence showing the (Maricopa County Sheriff's Office's) pattern and practice of racial profiling and its conducting of operations for reasons that are racially biased," Stan Young, lead attorney for those who filed the lawsuit, said in a written statement.
Arpaio won a small victory when the judge dismissed part of a claim by a Hispanic couple who are among the five people who filed the lawsuit.
Snow ruled that one of Arpaio's deputies had probable cause to pull over the couple on a closed roadway. The couple's illegal search claim was thrown out, but the judge didn't dismiss their racial profiling claim.
Messages left for Arpaio's lawyers weren't immediately returned late Friday.
The lawsuit alleges that Maricopa County officers made some traffic stops solely because Hispanics were driving. The plaintiffs say authorities had no probable cause to pull them over and made the stops only to question their immigration status.
Arpaio has denied the racial profiling allegations, saying people pulled over in the patrols were approached because deputies had probable cause to believe they had committed crimes and that it was only afterward that deputies found many were illegal immigrants.
During the patrols known as "sweeps," deputies flood an area of a city in some cases, heavily Latino areas over several days to seek out traffic violators and arrest other offenders. Illegal immigrants accounted for 57 percent of the roughly 1,500 people arrested in the 20 sweeps conducted by his office in earnest since January 2008.
Separate from the lawsuit, the U.S. Department of Justice issued a Dec. 15 report that accused Arpaio's office of having a pattern of racially profiling Latinos, basing immigration enforcement on racially-charged citizen complaints and punishing Hispanic jail inmates for speaking Spanish.
Arpaio faces a Jan. 4 deadline for saying whether he wants to work out an agreement to settle the civil rights allegations. The Justice Department has said it's prepared to sue Arpaio and let a judge decide the matter if no agreement can be worked out.
The Justice Department report prompted U.S. Department of Homeland Security to strip Arpaio's office of its federal powers to verify the immigration status of jail inmates. The severing of those ties came after an October 2009 decision by Homeland Security to take away the federal immigration arrest powers from 100 of Arpaio's deputies.
Arpaio is left with only state immigration laws to carry out his patrols and those powers were limited by the judge Friday.
Lawyers pressing the racial profiling lawsuit say considerations of race have infected the sheriff's immigration patrols and that Arpaio has, in effect, endorsed calls for racial profiling.
They say some of Arpaio's deputies circulated offensive jokes about Mexicans and that Arpaio launched immigration patrols based on racially charged letters and emails that complained of people speaking Spanish but alleged no actual crimes.
Arpaio's lawyers said the sheriff's office launches its sweeps on race-neutral grounds and that the sheriff never acted on those letters of complaint.
The judge also laid out punishments against Arpaio's office for its acknowledged destruction of records in the case, reprimands that come in the form of "adverse inferences" against Arpaio's office that the judge may consider when deciding the case's facts.
The judge, for instance, may assume that among the destroyed documents were citizen complaints some of which were racially-charged and didn't allege criminal activity that requested immigration patrols in spots where the sheriff's office later conducted patrols.
Apart from the lawsuit and civil rights report against the sheriff's office, a federal grand jury also has been investigating Arpaio's office on criminal abuse-of-power allegations since at least December 2009.
Grand jurors are examining the investigative work of the sheriff's anti-public corruption squad.