Police in south China's Guangdong Province have detained four suspects and launched a pursuit for three others who were allegedly involved in attacking a group of unpaid migrant workers, killing one of them, earlier this month.

After posting an online wanted notice for the three fugitives, police in Yingde City confirmed on Thursday that the alleged assailants were all from the No. 15 Bureau of the China Railway Construction Corp., contractor of the Guangzhou-Lechang Expressway Construction Project. The contractor had employed the migrant workers since September 2013.

The man who was killed has been identified as Zhao Zhiming, who was among the 21 migrant workers attacked by dozens of assailants, who wielded knives and iron bars, on a street about 10 minutes' walk from the construction project office, on March 6.

Police investigation has found that the workers were dismissed by the employer without payment after the Spring Festival holiday in February. They were refused payment again at the construction site office on March 6, and a short while later they were attacked by assailants who drove three vehicles to chase them down the road.

Zhao Xinbiao, uncle of the dead man, said the contractor owed his nephew 8,000 yuan (1,287 U.S. dollars) in salary. The group of migrant workers together claimed 140,000 yuan in unpaid salary.

Zhao said the workers had nothing personal against Li Yukun, the man alleged to have led the attack against the unarmed workers.

Detectives with the Yingde Bureau of Public Security confirmed that Li, a resident of Yingde City, was the material contractor for the construction project.

A deputy manager of the project, Zhao Ping, denied that the project office was involved in inciting Li and others to attack the workers. But he admitted the office was responsible for "improper management" of the construction project.

Delayed salary and labor abuse have been frequent occurrences in construction sites of big infrastructure projects contracted by state-owned firms like China Railway Construction Corp.

There have been dozens of reports of beatings targeting migrant workers claiming unpaid salaries nationwide in the past few years. All the cases implicated the project contractors in hiring hatchet men to use violence with the aim of intimidating the workers to give up their salaries.

Zhao Yongqi, a labor union official with the No. 15 Bureau of the China Railway Construction Corp., said although the company did not have "direct liability" for the beating, it is planning to provide 180,000 yuan as a "one-off compensation payment" to Zhao Zhiming's family.

A Yingde City government official, who declined to be named, said in the case of labor disputes involving big state-owed firms, local authorities often refrain from getting involved, as chief executives of these firms often have higher ranks than local officials.

Very often, workers' families are offered money to keep quiet.