But even given these challenges, the skepticism shown by police and prosecutors—who are not juries, after all—is extraordinary. Officials don’t talk about their methods publicly, and rarely reveal their thinking, much less their motives or biases. But two cities—Detroit and Los Angeles—allowed researchers to read thousands of pages of police reports and to interview detectives and prosecutors. What the researchers found is a subterranean river of chauvinism, where the fate of a rape case usually depends on the detective’s or (less often) prosecutor’s view of the victim—not the alleged perpetrator.

Usually only a certain type of victim will see her rapist prosecuted, says Cassia Spohn, the director of the School of Criminology and Criminal Justice at Arizona State University. Along with Katharine Tellis, a criminologist at California State University at Los Angeles, Spohn published an exhaustive report in 2012 that analyzed sexual-assault investigations and prosecutions in Los Angeles County. “We heard over and over detectives use the term righteous victim,” she told me. A woman who didn’t know her assailant, who fought back, who has a clean record and hadn’t been drinking or offering sex for money or drugs—that woman will be taken seriously. Spohn recalled a typical comment: “ ‘If I had a righteous victim, I would do all that I could to make sure that the suspect was arrested. But most of my victims don’t look like that.’ ”

In cases of acquaintance rape, detectives expressed doubt and blamed the women. They spoke skeptically of “party rapes,” in which women drink too much “and make bad choices.” One described “buyer’s remorse,” where a woman who has been out partying has sex with a man “willingly” and later regrets it. “Out of 10 cases,” one detective said, “eight are false reports.”