SHANGHAI, Feb. 28 -- The Shanghai Police on Saturday handed a local procuratorate a case alleging executives from 21st Century Media Ltd., and some public relations firms had engaged in criminal activity.

More than 30 suspects including Shen Hao, former president of the media group, will be investigated over suspected crimes including forced transactions, blackmail, duty encroachment and accepting bribes.

According to the police investigation, since 2009 the 21st Century Business Herald, a website affiliated with the publication "Money Week", and seven companies under the group, had partnered with public relations firms in Shanghai and Shenzhen to publish negative reports on listed companies and those planning initial public offerings (IPO).

The investigation found evidence that hundreds of enterprises had been forced to sign "cooperation" agreements, and told to pay "protection fees" to avoid negative coverage.

Police found Shen set high performance targets, encouraging the practice.

Shen was detained by police in September 2014.