Prosecutors will investigate five police officers involved in the controversial death of a man during an anti-prostitution operation in Beijing, the Beijing Municipal People's Procuratorate announced on Wednesday.

Legal experts and the public have welcomed the long-delayed move, hailing the prosecutors' decisive response to public outcry over what the police initially described as a death caused by the man's sickness following his forceful arrest for allegedly visiting a brothel on May 7.

However, experts also warned that the public should refrain from attempting to influence the judicial process, as the probe does not necessarily mean they are guilty.

The Beijing Municipal People's Procuratorate said that after a primary investigation into the case, five police officers, including one surnamed Xing, from the Dongxiaokou Police Station in Changping district, have been formally put under investigation for their alleged involvement in the death of Lei Yang.

The Beijing Municipal Public Security Bureau said on its official Sina Weibo on Wednesday that the Beijing police will coordinate the investigation of the procuratorate.

The Ministry of Public Security also said on its website Wednesday that it will impartially respond to public concerns involving police officers, and will not protect those in the wrong during law enforcement. It also vowed to punish those who defame the police's lawful duties.

Lei, a 29-year-old Beijing resident and father of a new born, mysteriously died on the night of May 7, when he was detained during a raid on a foot massage parlor suspected of being a brothel in Beijing, raising suspicions of police brutality and abuse of power, with many demanding an impartial investigation.

Changping police said on May 9 and 11 that Lei had violently resisted police arrest and tried to escape even after being placed in a police car, so the officers had to use "coercive restraint measures" to control him. He suddenly fell ill and was proclaimed dead after police sent him to a hospital, the statements said.

The case sparked a national outcry, as many fear that the police, if left unchecked, could lead to more people suffering a similar fate.

"The formal investigation of the five police officers means the procuratorate has  made some progress during the initial investigation," Wang Sixin, law professor at the Communication University of China told the Global Times on Wednesday.

"The Beijing procuratorate's timely handling of Lei's case highlights its impartiality under the law," Chen Youxi, the lawyer representing Lei's family, told the Global Times.

"The timely investigation [of the police officers] shows that the country's judicial system is effective," Chen said.

"Regardless of whether they are law enforcers or average people, as long as they break the law, they will be held responsible," he said.

However, some scholars lamented the delay in the formal investigation.

"Although we commend the formal investigation, it could have been done earlier," Wang Zhenyu, deputy director of the Public Decision-Making Research Center at the China University of Political Science and Law told the Global Times on Wednesday, adding that the delay could lead to loss of important evidence.

Chen also called for an online discussion of Lei's case, which he said can help with "legal education."

In the first few days following Lei's death, some posts questioning the police account of Lei's death were reportedly removed from Chinese social media.

Call for sobriety

However, some scholars cautioned possible public interference in a legal procedure.

"Because the facts remain unclear and the evidence insufficient, it is not proper to have an open discussion of the case, which might pressure judicial authorities," Wang Sixin said, adding that the public should stay calm and cautious.

"All sides should calm down, because only five police officers are involved in the case, and their legal rights should be respected," Wang Sixin said.

"Much remains to be investigated, including the alleged police brutality and how Lei died," he added.

Chen said he hopes for a timely release of the autopsy results for the sake of Lei's family, so that the lawyers could further study the case.

"We want to know the facts so that future incidents involving the police can be avoided," Wang Zhenyu said.