What happened in that bathroom is unclear, Bright said. A doctor who examined the woman could not say if she was raped, and while some DNA was found, there was not enough to determine whom it belonged to.
"We are not condoning Mr. Roethlisberger's actions that night," Bright said. "But we do not prosecute morals. We prosecute crimes."
He said local and state investigators spent weeks questioning witnesses even though the woman sent a letter urging prosecutors not to move forward with charges.
"I know when I have a case and I know when I don't," Bright said. "And I do not have enough evidence to convince 12 jurors beyond a reasonable doubt that Mr. Roethlisberger was guilty of rape."
Bright said the woman told him it had been an "unnerving experience" and that she and her family made it clear they did not want the matter prosecuted.
Lee Parks, the woman's attorney, did not immediately comment.
Roethlisberger was seen out with a few friends at several different bars that night. The Capital City club is a popular spot for students at the neighboring Georgia College & State University. Roethlisberger owns a home about 30 miles north on Lake Oconee, in central Georgia.
The two-time Super Bowl champ is being sued by a different woman who says he raped her in 2008 at a Lake Tahoe hotel and casino, an allegation he denies. Roethlisberger has not been criminally charged in that case either and has claimed counter-damages in the lawsuit.
Roethlisberger has not taken part in recent offseason workouts with the Steelers.
As Pittsburgh's first-round draft pick out of Miami of Ohio in 2004, Roethlisberger led the Steelers to Super Bowl victories in 2006 and 2009. He frequently has donated time and money to charities, and his charitable foundation awards a police dog to a department near every Steelers road opponent.
But off-field problems have come along with his championships and $102 million contract. In 2006, he defied his coach's orders and rode his motorcycle without a helmet -- and wound up with a concussion, broken jaw and other injuries after a wreck.
And while Roethlisberger has a reputation for patiently signing autographs and posing for pictures while out in public, he also is known for occasionally inelegant behavior in Pittsburgh.
Early in his career, he was photographed -- obviously after drinking -- wearing a T-shirt reading "Drink Like a Champion."