Why it's so hard to prove racial profiling.

AZ - Legal experts warn that lawsuits claiming racial profiling by police officers — one of the avenues that Justice Anthony Kennedy listed as a way to challenge the law — take a long time to develop and are difficult to win.

"The court has all but said, 'We're watching you. All the courts are going to be watching you.' But it is difficult to do these cases even in the best of circumstances," says David Harris, a professor at the University of Pittsburgh School of Law who has testified before Congress on racial profiling issues. "The proof is painstakingly built, and it takes time."
How much time?
"At least six months or a year," he says.
The court struck down three provisions of the Arizona law that created state crimes targeting illegal immigrants and expanded the power of local police to perform warrantless arrests of people who could be deported. 
The court upheld a provision that requires state and local officers to check the immigration status of anyone they stop or detain if a "reasonable suspicion" exists that the person is in the country illegally.In the majority opinion, Kennedy wrote that the court's decision to uphold it "does not foreclose other pre-emption and constitutional challenges to the law."
Getting those constitutional challenges against the law into the court system isn't easy. 
Complaints of racial profiling against Maricopa County (Ariz.) Sheriff Joe Arpaio in the Phoenix area show how difficult the process can be.
In June 2008, the Justice Department initiated a civil rights review of Arpaio, who has made immigration enforcement a focus of his department and routinely conducts roundups throughout the county. It wasn't until May that the department decided it had enough evidence to sue Arpaio's office.A separate class-action lawsuit against Arpaio, initially brought by several Latinos who are either U.S. citizens or legal residents, was filed in December 2007. A federal judge granted a preliminary injunction, forbidding Arpaio's deputies from enforcing some immigration laws, in December. The case is scheduled for trial this month.
Throughout those years, the Justice Department and lawyers for the plaintiffs in the lawsuit amassed accounts of harassment and statistics bolstering their case that Arpaio's deputies pull over Latinos more often than non-Latinos. The Justice lawsuit alleges that Latinos in Maricopa County are three to nine times more likely to be pulled over than non-Latinos.
"In the whole time that evidence has been building … Latinos have been facing the very real horror of being nine times more likely of being stopped," said Karen Tumlin, managing attorney for the National Immigration Law Center, one of the groups suing Arizona. "That's the downside of the kinds of proof required in these kinds of cases."
In court documents, Arpaio's attorneys denied all allegations of racial profiling and said Maricopa County deputies have acted "reasonably, constitutionally and lawfully at all times."
http://www.usatoday.com/news/nation/story/2012-07-11/racial-profiling-arizona-lawsuit/56150978/1