Police in Central China's Henan province have brought 95 people implicated last month in a tainted pork scandal into custody and have successfully solved the case, Henan public security authority announced over the weekend.

The Henan police said they have ceased to investigate the case, which began with the discovery that the Henan-based Shuanghui Group, China's largest meat processor, had bought pigs fed with clenbuterol, an illegal additive also named "lean meat powder".

Clenbuterol helps pigs burn fat and results in leaner and more expensive meat. It can cause heart palpitations and dizziness in people. In China, the substance has been banned as an additive in animal feed since 2002.

The illegal factory where the clenbuterol was produced has been closed, a senior official with Henan's public security department, who requested anonymity, told Xinhua News Agency.

The police seized 14 suspects on March 15, when a subsidiary of Shuanghui was first found to have used the additive. By March 29, the police had taken into custody every suspect believed to be a party to the case, including producers, sellers and buyers of the drug. The suspects hailed from Hubei, Henan, Shaanxi and Jiangsu provinces.

According to the official, the clenbuterol in Henan was produced in a chemical factory in Baquan village of Xiangyang city, in Hubei province.

One of the chief suspects, surnamed Liu, worked in the factory and was in charge of a workshop. He secretly produced clenbuterol in addition to doing his daily work. Nobody in the plant knew of his covert undertakings until the police arrived on March 22.

Liu, 42-years-old, majored in chemistry and once worked in a pharmaceutical factory. In 2007, a man named Xi from Jiangsu, another chief suspect, asked Liu to cooperate and manufacture the "profitable additive". Liu used the workshop in the chemical factory and succeeded in producing clenbuterol by himself after four months of experimenting.

Liu told the police he made a fortune by selling the drug at a price of 2,000 yuan (US$306) a kilogram to Xi and another buyer from Henan, surnamed Chen. That buyer added starch to the chemical and sold it to middlemen, who then turned around and sold it to the final buyers -- farmers who raise pigs.

The police have arrested Chen and Xi. Other suspects in custody include three purchasing workers from Shuanghui.

Last week, prosecuting authorities began investigating 12 government officials implicated in the case to ascertain whether they had been derelict in their duties.

About 18 tons of pig feed suspected of containing clenbuterol were confiscated by the authorities during a check that lasted from March 15 to 23, according to Henan police.

The province also conducted urine tests on 1,512 pigs in nine pig farms. Of those pigs, 52 tested positive for clenbuterol.

Wan Long, chairman of Shuanghui Group, apologized to consumers after the scandal, blaming the case on the examination system, which he said "could not be 100% accurate".

Responding to the scandal, the Ministry of Agriculture vowed on Sunday to strengthen its supervision of the quality and safety of animal products.