BEIJING  There was a time when the story of the 21-year-old waitress who fatally stabbed a Communist Party official as he tried to force himself on her would have never left the rural byways of Hubei Province where it took place.

Instead, her arrest last month on suspicion of voluntary manslaughter erupted into an online furor that turned her into a national hero and reverberated all the way to China’s capital, where censors ordered incendiary comments banned. Local Hubei officials even restricted television coverage and tried to block travel to the small town where the assault occurred.

On Tuesday, a Hubei court granted the woman, Deng Yujiao, an unexpectedly swift victory, ruling that she had acted in self-defense and freeing her without criminal penalties.

The case of Ms. Deng is only the most recent and prominent of several cases in which the Internet has cracked open a channel for citizens to voice mass displeasure with official conduct, demonstrating its potential as a catalyst for social change.