The number of annual reported sexual assaults in prisons and jails has tripled from 2011 to 2015, according to a new report from the Bureau of Justice Statistics, bringing the overall rate of reported assaults from 3.9 per 1,000 inmates in 2011 to 11.0 per 1,000 in 2015. That increase is not necessarily because of a jump in actual assaults but rather legal changes that have made inmates more aware of the resources available to them following an assault.

The Prison Rape Elimination Act, which finally went into full effect in 2012 after its initial passage in 2003, mandates that incarcerated people be educated about their right to report a sexual assault. According to Prison Legal News, under the PREA, prison officials must make clear that inmates will not risk punishment for filing a sexual assault claim “in good faith based upon a reasonable belief that the alleged conduct occurred.” These standards have led to a surge in reporting — the number of official allegations leapt from 8,768 in 2011 to 24,661 in 2015.

Still, an untold number of incarcerated people continue to fear reporting that they have been raped, in part because investigations rarely ever confirm the initial assault. Only 8 percent of allegations are ever proven, according to the report from 2015.

That isn’t because inmates are lying about their assaults, Lovissa Stannow of the advocacy group Just Detention International told The Marshall Project. “Prisoners have nothing to gain from filing false sex abuse reports,” she said. The more likely explanation is that the investigations themselves have been inadequate.

Guards facing sexual assault allegations are much more likely to be absolved of responsibility than inmates who face the same allegations. While sexual assaults by staff account for the majority of reported assaults (58 percent), of the substantiated claims, only 42 percent were those made against staff members. Stannow put it like this: when it comes to investigating officials accused of sexual assault, “there’s a very strong tendency to close ranks.”