author of ` into the wild ' spoke to five rape victims in missoula , montana .
` missoula : rape and the justice system in a college town ' was released april 21 .
three of five victims profiled in the book sat down with abc 's nightline wednesday night .
kelsey belnap , allison huguet and hillary mclaughlin said they had been raped by university of montana football players .
huguet and mclaughlin 's attacker , beau donaldson , pleaded guilty to rape in 2012 and was sentenced to 10 years .
belnap claimed four players gang-raped her in 2010 , but prosecutors never charged them citing lack of probable cause .
mr krakauer wrote book after realizing close friend was a rape victim .