A lawyer for the plaintiffs who filed a civil lawsuit against Arpaio's department said in opening statements that the evidence will show that Arpaio and his deputies discriminated against Hispanics.
"It's our view that the problem starts at the top," attorney Stan Young said.
Tim Casey, who is defending Arpaio, said the patrols were properly planned out and executed. He said they exceeded police standards. "Race and ethnicity had nothing to do with the traffic stops," Case said.
Arpaio has said people pulled over were approached because deputies had probable cause to believe they had committed crimes and that officers only learned afterward that many were illegal immigrants.
The plaintiffs aren't seeking money damages. They want a declaration that Arpaio's office racially profiles and an order that requires the department to make changes to prevent what they said is discriminatory policing.
The lawsuit will serve as a precursor to a U.S. Justice Department's case that alleges a broader range of civil rights violations by Arpaio's office. A DOJ lawyer leading the agency's civil rights case watched the trial.
Arpaio, who didn't appear in court Thursday, is expected to be called to testify Tuesday.
For years, Arpaio, the self-proclaimed toughest sheriff in America, has vehemently denied allegations that his deputies in Arizona's most populous county racially profile Latinos in his trademark patrols.
The plaintiffs say deputies based some traffic stops on the race of Hispanics who were in vehicles, had no probable cause to pull them over and made the stops so they could ask about their immigration status.
David Vasquez, an IT specialist from Mesa who identified himself as a Mexican American, said he and his wife were pulled over during a June 2009 sweep as the couple was headed to dinner. One of the deputies who stopped them asked Vasquez whether he spoke English, which he does.
"I just found it funny that he asked me that question because I felt like I had been singled out. I've never been asked that question," Vasquez said. He said he was following the speed limit and hadn't broken any traffic laws.
Five or 10 minutes after being pulled over, a deputy said he pulled Vasquez over because he had a crack in his windshield, which Vasquez testified wasn't blocking his view of the road.
The officer didn't write him a ticket. Vasquez now questions how the officer was able to spot the crack in the windshield given his position at an intersection.
After the officers let him go, Vasquez said it occurred to him that he was just racially profiled and told his wife: "I believe I was pulled over for being brown."
Under questioning from an Arpaio attorney, Vasquez said he didn't report the traffic stop to authorities and was contacted months later by Arpaio critics who had video-recorded the stop.
Another man who was Hispanic testified about being pulled over by a sheriff's deputy in December 2007.
David Rodriguez said the deputy pulled him over as Rodriguez and his family had just been off-roading in the area and had ended up driving on a closed road. Rodriguez said other drivers who were also on the road and who were white were let off with only a warning, while he was ticketed.
Rodriguez said the officer asked him for his Social Security card, in addition to his driver's license and registration and proof of insurance for his truck. Asked why he believed he was treated differently, Rodriguez said, "Because I'm Hispanic."
Questioning by Arpaio's lawyer suggested that the deputy had asked for only Rodriguez's Social Security number for the purpose of completing a part of the citation form and that the other drivers in the area were allowed on the closed road to survey damage to property caused by a storm.
The lawsuit echoes some of the racial profiling accusations in the DOJ case. That suit said Arpaio's office retaliated against its critics, punished Latino jail inmates with limited English skills for speaking Spanish and failed to adequately investigate a large number of sex-crimes cases. No trial date in that case has been set.
Arizona State University law professor Carissa Byrne Hessick said that if Arpaio loses the current case, the verdict would likely stand as the finding on whether Arpaio's office racially profiles.
The sheriff likely wouldn't be able to re-litigate the profiling allegations in the DOJ case. Still, Arpaio could dispute the other allegations, Hessick said. If Arpaio wins, the DOJ wouldn't be prevented from bringing its racial profiling allegations to trial.
The judge overseeing that case might be inclined to rule against the federal agency on the racial profiling claim because there would be a fellow judge who concluded that