Transcript for Inside 'Missoula' Campus Rape Investigations: Part 2
Back now with the women on a crusade to confront what they believe is a rape cry skis on college campuses. One victim making a crucial discovery that could help to seal her attacker's fate. The other confronting a nightmare that her own account of the blurry night maybe turned against her. I felt so violated. I was like no, no one is going to get away with doing this to me. Reporter: It had been two months since Kelsey said she was gang raped at a drunken off campus apartment inside of this apartment by football players. How incapacitated do you think you were? So drunk I don't remember if what was going through my mind. Thinking I need to get the hell out of here an I couldn't move. Reporter: After an investigation, detectives and prosecution determined there was not probable cause to file criminal charges against anyone involved in the understand sglent case closed. What was your reaction in. Shocked. I was like, this I thought to myself this is a slam dunk case. Missoula police report. A case that highly acclaimed author Jon Krakauer followed through every twist and turn in his new book. Any of the boys or the girl in the situation said it is all covered up. Reporter: Investigators pointed out that a crucial part of Kelsey's own testimony was working against her, on the question of consent, Zell Kelsey told police the men would have believed it was consensual sex. She stated she was so intoxicated she didn't resist them. The football players and two additional witnesses said they thought the sex was consensual. The cop who investigated, the detective told her, Kelsey, it's your word against six people. How am I supposed to work with that. Reporter: Montana law says a victim is incapable of giving consent if they are mentally defective or incapacitated but the definition is murky and the county attorney insists despite being extremely drunk, Kelsey was not legally incapacitated. The cops and prosecutors said if she had been out cold, yeah, you would have a case. Because she was in and out of consciousness she doesn't have a case. That is horse . That is ridiculous. Reporter: Prosecutors considered the evidence as insurmountable hurdles in her case. Even though she told police she was afraid to fight back. I was scared because these boys were a lot bigger than me. I didn't matter how hard I would have fought. Reporter: The attorney general's office agreed with the prosecutor's decision not to file charges in Kelsey's alleged gang rape. The federal justice department found cases like Kelsey's were part of a pattern and they declined to prosecute cute every case where there was drugs or alcohol. Prosecutors filed charges in only 14 of the 85 total rape cases the police sent them. They have never been done this to any prosecutor. Reporter: The missoula county attorney at the time disputed the doj's findings and defended their record saying their prosecution stats are on par with other major cities. That's what is so insidious and I think this is true in most cities. So the prosecutor puts out this message, we're not going to do it unless it is so glaringly obvious we have to do it. After Kelsey hit a dead end with police and prosecutors, she turned to the university for justice. Of the four football players, one was expelled, one agreed to leave and two left school before the university could take action. What goes through your mind as you walk down this alley? I think it is surreal because I don't -- for me it was dark and I don't recall a lot of this. It had been nearly two years of anxiety and anger since Allison Huguet was raped by beau Donaldson. After a secretly recorded audio confession. Something I did and I Up. Reporter: And police investigation beau still was not behind bars. Then a stunning twist. He came in his shorts and underwear and got on top of me. Reporter: Hillary Mclaughlin who says she was sexually assaulted by beau Donaldson two years before Allison's attack but she never reported it to police. Does it occur what might have happened if you tried to press charges? It kills me because I could have possibly prevented what Allison went through. That brings a lot of guilt. Her life could have been different if I had the courage to say this person was wrong and tried to hurt me. He needs -- something needs to be done about it. Reporter: When Allison found out about Hillary she tipped off detectives and they convinced her to tell her story in court. That was huge. Puts a lot more doubt on his stories and gives me more credible. That was huge. Reporter: In September 2012, beau pled guilty to Allison's rape. The front page story divided griz nation. Tell me about the backlash for people who come forward and report rapes. It's awful. People are awful. She just kept crying. Reporter: In court, beau had to listen to gut-wrenching statements from Allison and her loved ones. I just said that he thought he deserved to be raped every day until he could understand what he was putting me through. Reporter: He was sentenced to ten years in prison. He will be up for parole this July. I think we all have this misconception that a rapist is somebody wearing a ski mask and carrying a weapon. Beau is a rapist, that's what a rapist looks like and the ones that look like beau are scarier because you are more likely to let your guard down. Reporter: In the the wake of the dod the doj investigation, they formed groups. His new book has opened old wounds in missoula. At a press conference today the current county attorney who he criticizes in the book shot back at the author. The charges that the author has made against me, my office, my predecessor are inaccurate, exaggerated and unnecessarily personal. He is correct in that our investigation and prosecution standards needed to be improved. Reporter: As for the university, among a host of other reforms the athletic department created a code of conduct that directly addresses sexual assault. Missoula is much safer place for women now than when I looked at it in 2012. Reporter: But for him he said the most important part is it finally gave victims a voice. More women are seeing there's strength in Numbers. The rapist's greatest weapons they use against victims is silence. I'm sick of being silent. I feel like I can be a voice for so many people who don't have that chance to be that voice for themselves. Reporter: Jon Krakauer's book, "Missoula: Rape and the justice system in a college town" is available now.
This transcript has been automatically generated and may not be 100% accurate.