Ajay Chaudhary, 24, was killed point-blank range allegedly by armed men near his house in city's Sector 8 on the night of October 4, they said.
His death followed two protests the next day by right wing groups, including the Bajrang Dal and the Vishwa Hindu Parishad, demanding compensation for the family and an accommodation.
The protests witnessed traffic snarls along with law and order situation, prompting the police to use baton and tear gas shells to quell the mob.
An FIR for murder and related offences was registered against eight people, six of them named and two unidentified, at the Sector 20 police station with the police nabbing three accused within 12 hours.
He said the police will now appeal in the court for his custody, while searches were underway to arrest the other accused in the case.
According to Chaudhary's family, he was killed for repeatedly complaining to the police about illegal activities of the accused identified as Shehzaad, Ashraf, Zafar, Sartaj, Rafeeq, Jeetu Yadav, Sitabuddin Ansari, and two unidentified men.
Three of them -- Zafar Ali, Sitabuddin Ansari and Sartaj Khan -- were arrested on October 6, the day scores of protesters staged a demonstration at Sector 20 police station, alleging "police inaction" in the matter.
According to Vijay Chaudhary, his brother Ajay had made several complaints with the police as well as local authorities about the accused running betting racket, illicit liquor trade, drug trafficking and other illegal businesses.
The police had initiated a departmental inquiry into the allegations of inaction and suspended the in-charge of a police post, according to officials.
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