Three senior police officers in Qingdao, Shandong province, are being investigated on bribery charges that are believed to be linked to a major gang case in 2010.

Prosecutors have detained Zhao Min, head of the anti-terrorism division at the city's Public Security Bureau, and two deputy crime squad heads.

A total of 53 officials were implicated following a crackdown on an organized crime group headed by Nie Lei in September 2010. Many of them were in the city's political and legal departments.

Nie, 44, was executed in September of last year after being tried on charges including involvement in prostitution activities, gun smuggling and deliberately causing injury. It was Qingdao's largest gang-related case.

After Nie was arrested, two heads of police bureaus in the city's Shibei and Licang districts and scores of other officers were prosecuted for providing protection for Nie's illegal gambling and drug businesses.

Wang Yanqiu, former deputy head of the city's Political and Legal Affairs Committee, was sentenced to 15 years in prison for taking bribes of 1.98 million yuan and covering up the gang crimes. Property worth 200,000 yuan belonging to Wang was confiscated.

He was in charge of wiping out prostitution in the city but was convicted of covering up Nie's involvement in organizing this trade.

Those convicted of organizing prostitution can face a life sentence or the death penalty, while workers and clients in the sex business can face up to 15 days' detention and a fine of up to 5,000 yuan.

Wang Yongli, the city's former police chief, has been placed under investigation since 2012 for taking bribes.

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