A federal judge has ruled that New York City's "stop-and-frisk" program — a major part of city law enforcement — is being conducted on vague, irresponsible, and sometimes unconstitutional grounds, charging an outside monitor with helping overhaul it. In an opinion delivered today, Judge Shira Scheindlin vindicated the system's many critics, saying there was solid evidence that New York police unfairly targeted black and Hispanic pedestrians based on often baseless suspicions.

Impromptu stop-and-frisk searches are meant to let New York police officers quickly investigate people they think may carry drugs or weapons. Mayor Michael Bloomberg has staunchly defended the practice, crediting it in part for a decrease in crime. He quickly dismissed complaints that black and Hispanic people were subject to a disproportionate amount (87 percent, according to a recent statement) of searches, saying that if anything, they should be stopped even more often based on crime statistics. Opponents, however, have pointed out that whatever the racial disparities in violent crime, most searches find no evidence of wrongdoing: in 2008, only 6 percent of stops ended in an arrest.

After hearing testimony and evidence from several men and one woman who believed they had been targeted due to race, Scheindlin found that the NYPD's procedures sometimes deprived them of "basic freedom" guaranteed by the Fourth Amendment. Even when controlling for other factors, police were more likely to conduct stops heavily in black or Hispanic neighborhoods, used force less often with whites, and stopped "suspicious" black or Hispanic with weaker justifications: white suspects, for example, were proportionately more likely to actually be carrying a weapon.

She also dismissed Bloomberg and police chief Ray Kelly's argument that since blacks and Hispanics make up most violent crime suspects, they should be targeted more often. "The fact that the targeted racial groups were identified based on crime victim complaints does not eliminate the discriminatory intent," she wrote. "It is impermissible for a police department to target its general enforcement practices against racially defined groups based on crime suspect data." In fact, the NYPD's "willful blindness" towards individual officers' bad judgment counted strongly against it. "Despite frequent and ongoing notice of troubling racial disparities in stops, the NYPD has long shown its lack of concern for racial profiling," she said.

Scheindlin said that she was emphatically not banning the stop-and-frisk program, but she insisted that it must be brought "into compliance with the Constitution." Police can no longer stop people for being in a "high crime area," nor can they do so only because of "furtive movements," one of the largest driver of stops and one that's far more likely to be applied to blacks and Hispanics. She also said that police had been routinely misinterpreting the law. "The purpose of a frisk is not to discover evidence of crime, but to allow the officer to pursue his investigation without fear of violence," she said. Changes at the NYPD will be overseen by attorney Peter Zimroth, a former federal prosecutor who has served in several parts of New York's legal system.

Scheindlin's reforms strike at a core part of Bloomberg's police strategy: the idea of targeting groups that are believed more likely to commit crimes. If police are looking for a specific suspect, race is just as relevant as hair color or height, but otherwise, she categorically rejected the idea of looking for "the right people," a phrase used by defenders of stop-and-frisk. "In particular, officers must cease the targeting of young black and Hispanic males for stops based on the appearance of these groups in crime complaints," she wrote.

While the ruling will directly affect a particular part of New York City policy, it's also a larger statement on American law enforcement, which many say disproportionately relies on racial statistics or stereotypes to enforce the law. After September 11th, New York police routinely used surveillance cameras or informants to target wide swaths of the Muslim population, and unified surveillance efforts, which are becoming both more common and more powerful, can amplify the effects of any single bad decision.