BEIJING, July 10 (Reuters) - The southwest Chinese town that erupted in rioting late last month was a powder-keg of corruption, unchecked crime gangs and public anger, the area's former police chief has said.

The violent protest brought 30,000 residents onto the streets of Weng'an, in Guizhou province, in an unnerving outburst of discontent as China prepares to host the Olympic Games in August.

Crowds torched police and government buildings and smashed official cars on June 28 after allegations spread that police had covered up the rape and murder of a local teenage girl, seeking to protect the son of a local official.

State media on Thursday said that the latest, third autopsy on the 16-year-old victim, Li Shufen, did not reveal any evidence of sexual assault or murder, and showed she died by drowning.

But the recently sacked chief of the Weng'an County Public Security Bureau, Shen Guirong, told the China Newsweek magazine that local residents already had plenty to be angry about before the junior secondary student's death.

"Our authority was gone long ago. Our offices were often attacked," Shen said in an interview published in the latest issue of the Chinese-language magazine.

Discontent with policing in Weng'an grew because of growing unsolved crimes, including a series of four explosions in the town late last year, and because police harshly quelled protests over dam resettlement, disputed mines and forced home removals.

Angry residents had surrounded and attacked rural government and police offices in earlier clashes, Shen said. Local crime gangs involved in gambling and drugs also bought off local police, he said.

"Though I didn't get to the bottom of who had been corrupted, I can say with certainty that there was collusion inside public security with crime gangs," he said, citing a raid on a gambling den that fizzled after the operators found out beforehand.

China, with its vast and poor rural population, sees many thousands of protests and what officials call "mass incidents" every year. But in the build-up to the Beijing Olympics, authorities want to stamp out any signs of unrest.

The official Guizhou Daily on Thursday reported that the provincial party boss, Shi Zongyuan, had urged local officials to ensure social stability and avoid inflaming discontent.

"Avoid unlawful and crude administrative ways," Shi said. "Guide the masses to express their demands in a rational and lawful way." (Reporting by Chris Buckley; Editing by Ken Wills and Alex Richardson) (chris.buckley@reuters.com; +86 10 66271261)

AlertNet news is provided by