China has invited skeptical Internet surfers to help investigate the death of a man in custody who police say ran into a wall blindfolded while playing hide-and-seek, state media said on Friday.

Li Qiaoming, 24, died from a severe brain injury four days after being sent to hospital from a detention center in the southwestern province of Yunnan, the Beijing News said.

He had been arrested for illegally cutting down trees.

The cause of death given by police has been widely questioned on the Internet.

We've invited Internet users to investigate the case on the spot and hope they can made their own judgment and spread the information they see with their own eyes to as many people as possible, Gong Fei, Yunnan's propaganda chief, was quoted as saying.

It's the first time in Yunnan, and even in China, netizens have been asked to participate in an investigation, he was quoted by the official Xinhua news agency as saying.

China, the world's most populous country, has the world's largest Internet population, with 298 million users at the end of 2008, an increase of nearly 42 percent from the previous year.

China keeps a tight rein over the Internet, launching crackdowns on what it sees as vulgar content, ranging from pornography to politically taboo subjects, but also keeps a close eye on hotly discussed topics for signs of possible unrest.

Police brutality of detainees to extract confessions is also a regular topic for the media.

(Reporting by Beijing newsroom; Editing by Nick Macfie and Sanjeev Miglani)

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