An attorney representing the woman contacted police in late 2006, said county District Attorney Michael Schrunk. Schrunk said the woman - who has not been identified - refused to be interviewed by detectives and did not want the investigation to proceed.
The woman, however, contacted police in January 2009 and gave a statement, saying Gore tried to have sex with her during an appointment at the upscale downtown Hotel Lucia, where Gore was reportedly registered as "Mr. Stone".
The National Enquirer first reported the allegations on Wednesday, identifying the accuser as a 54-year-old woman.
Gore family spokeswoman Kalee Kreider said the former vice president has no comment. Gore and his wife announced on June 1 they were separating.
A police report prepared in 2007 said the alleged incident happened at 2 pm local time on October 24, 2006. Gore was in Portland to deliver a speech on climate change.
The woman, according to the report, canceled appointments with detectives on December 21 and 26 of that year. Her attorney cancelled another meeting scheduled for January 4 and said the matter would be handled civilly.
"This case is exceptionally cleared as (the woman) refuses to cooperate with the investigation or even report a crime," the report states.
The case reopened in January 2009. Detectives interviewed the woman but determined there was insufficient evidence to support the allegations, Portland police said in a news release.
In a transcript of the interview released by the police, the massage therapist said she was doing requested abdominal work on Gore when he started to moan and demanded she go lower.
"I was shocked and I did not massage beyond what is considered a safe, nonsexual area of the abdomen," she said. "He further insisted and acted angry, becoming verbally sharp and loud."
"I went into much deeper shock as I realised it appeared he was demanding sexual favours or sexual behaviors."
She said Gore grabbed her hand and shoved it toward his pubic area. She alleged he later tried to have sex with her and began caressing her before she squirmed out of his grasp.
"I did not immediately call the police as I feared being made into a public spectacle and my reputation being destroyed," she said. "I was not sure what to tell them and was concerned my story would not be believed since there was no DNA evidence from a completed act of rape. I did not even know what to call what had happened to me."
Detective Mary Wheat, a police spokeswoman, said the woman contacted detectives this month and asked for a copy of her statement. The woman, according to Wheat, said she planned to take her case to the media.
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