After being acquitted of the charge of poisoning two children, Nian Bin, a former death row prisoner in Chinese southern province of Fujian, was set free three months ago.

Over the past eight years, his case has been tried, appealed, retried and re-appealed. He was sentenced to death four times.

In August, due to insufficient evidence to support the charges, judges in Fujian Higher People's Court ended this eight-year ordeal by declaring Nian not guilty.

Nian's case has become one of the most publicized trials across the nation, and the rare acquittal was proclaimed by many as a landmark event heralding a renewed commitment to the rule of law.

However, now the case is under the spotlight again. After three months' freedom, Nian has now been put under investigation once more, and his movement has been curbed by local police. This dramatic turn has proven highly controversial.

Media reports have prompted responses from local police,  asserting that this new investigation complies with legal procedures. However, Nian and his lawyer, along with people paying close attention to the case, suspect this is retaliation from the local police.

Re-investigating Nian will obviously cause a sensation, because after the acquittal was announced, an overwhelming consensus proclaimed the verdict as a victory for the "presumption of innocence," a legal principle which people are hoping will be more strictly followed in Chinese judicial system than before.

The overwhelming power of public opinion will denounce any attempt to think or do otherwise.

Nevertheless, technically speaking, an acquittal will not give Nian immunity from suspicion, because the closed poisoning case has now been re-opened.

In fact, according to Chinese laws, Nian can be charged again if the police investigation finds new evidence.

Nian could remain a suspect, but the risks are much higher as the police are now at a disadvantaged position in public opinion.

If their investigation produces nothing valuable and the real murderer remains at large, it can be expected that they be strongly criticized by the public, and the authority of the local law enforcement agencies will be undermined.

Any judgmental remarks may prove irresponsible, because so many mysteries remain to be unveiled.

The police cannot make an arbitrary determination that Nian is the murderer, but nor can public opinion insist that police are retaliating against Nian.

Justice is a result, not a tool   that can be manipulated in anyone's favor. It will be done, but not because of what people think, but because of what people did.

Qin Xianfa, a high school teacher based in Shenzhen