PHOENIX -- Only 31 percent of reported rapes cases in the Valley are solved, according to FBI data collected between 1990 and 2007.

“It's a very hard crime to solve because of the difficulty in getting evidence,” said Stephanie Orr, Executive Director for the Center for Prevention of Abuse and Violence.

Orr said the rape victim is usually the only witness to the crime.

“If there's only two people in a situation, then it's one person's word against another person,” she said.

DNA evidence is also often not enough to prove a woman was forced to have sex.

"It's very difficult to prove a rape when someone's already has consensual sexual activity in their life,” she said.

Orr said a woman may be bruised after an attack, but often shows no obvious signs of physical trauma, especially is she was drugged.

It often take months for DNA rape kits to be processed. A CBS investigation found Phoenix police did not know how many untested kits it had in storage.

"My DNA rape kit sat at the crime lab for eight months before it was even tested,” said Hilary Peele, a rape victim who frequently speaks out about her terrifying experience.

The former Miss Arizona and ASU graduated was raped in her Tempe apartment in 2004.

"I got into the shower. When I got out of the shower, I found that a man had broken into my apartment. He threw a towel over my head so I couldn't see his face. He held a knife to my throat and forced me into my bedroom and raped me at knife point for about 45 minutes,” she said.

To this day, her attacker has never been arrested.

"It's tough to know this man could come into my life, shatter it, destroy it, rip it to pieces, and then just walk away,” she said, “I've learned that my own closure with the rape is not going to rely on his capture because that may never happen.”