There's already some circumstancial evidence. For example that one women dragged out of the car with blood on her pants. I find it hard to believe that they murder, decapitate and so on but rape is a bridge too far. ISIS raped a lot as well and they are pretty similar. Plus the same people form rape gangs in Europe so ...I doubt it's true. I'm old enough to remember the whole Jessica Lynch thing where they acted like she'd been brutally gangraped for weeks on end in the US media only for it later to come out that Iraqi forces had just turned her over to a private doctor early on in her captivity and she was generally well treated.