Former Vice President Al Gore was cleared Friday of allegations he groped and assaulted a masseuse in a luxury Portland hotel room in 2006, closing a case that could have tarnished the Nobel prize winner's reputation.

After a four-week investigation that included interviews with Gore, masseuse Molly Hagerty, her acquaintances and hotel staff, as well as testing a pair of stained pants belonging to Hagerty, Multnomah County District Attorney Michael Schrunk said Friday there was no basis for prosecution.

In a memo to Schrunk released with the decision, Senior Deputy District Attorney Don Rees cited "contradictory evidence, conflicting witness statements, credibility issues, lack of forensic evidence and denials by Mr. Gore."

Rees also said Hagerty and her attorneys were uncooperative, witnesses could not remember anything unusual, Hagerty failed a polygraph examination and she would not say whether she was paid by a tabloid newspaper for her story.

Gore aides welcomed the news.

"Mr. Gore unequivocally and emphatically denied this accusation when he first learned of its existence three years ago," spokeswoman Kalee Kreider said in a statement. "He respects and appreciates the thorough and professional work of the Portland authorities and is pleased that this matter has now been resolved."

Gore and his attorneys met with Portland detectives in San Francisco on July 22, telling them he remembered almost nothing about the woman and was "completely baffled" by her statements, according to the memo.

Among the contradictory or conflicting statements about the alleged incident at the Hotel Lucia in downtown Portland on Oct. 24, 2006, prosecutors noted: