The man who was known for blowing the whistle on China's toxic milk products was killed during a domestic dispute and not in a revenge attack as previously suspected, police have said.

Jiang Weisuo, 44, was stabbed and injured on Nov. 2 during a dispute with his wife over his drinking habits, according to Tang Jianping, head of the Yanta branch of the Xi'an Municipal Public Security Bureau in northwest China's Shaanxi Province.

He later died in hospital, the police officer said.

The death of Jiang, who was the first to tell on the prevailing illegal practices in China's dairy industry in 2006, two years before media exposure on a major milk powder contamination scandal, had quickly aroused wide speculations that he might have been killed on revenge.

Police said six of the nine suspects involved in Jiang's death, including his wife Yang Ping and her younger sister Yang Caiying, have been detained over alleged assault. Yang Caiying's husband Lin Fan was also detained.

Yang Ping had confessed to the crime, according to Huang Lin, vice head of the Yanta branch of the Xi'an Municipal Public Security Bureau.

Jiang, who had been accused of beating his wife after drinking, had a dispute with Yang Ping in the early hours of Nov. 1, the police officer said.

Yang Ping turned to Yang Caiying, Lin Fan and others for help, Huang said.

The police said they were waiting for autopsy results to determine the cause of Jiang's death.

Jiang Weisuo, founder and general manager of Yanglinbaofeng Agriculture Science and Technology Development Company in Shaanxi, had faced great pressure after his whistleblowing in 2006.

He was called "black sheep" by his competitors in the dairy industry.

It was not till 2008, when the milk powder contamination scandal shocked the whole country, that Jiang earned himself the reputation of "hero" and "pioneer."

The melamine-tainted milk power resulted in the death of at least six babies and left 300,000 others ill in the country in 2008.

A number of Chinese officials were removed from their posts and scandal-tainted Sanlu Group, once a leading dairy producer in the country, went bankrupt following the exposure. Some members of Sanlu's management had been jailed.

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