RAB sought a 10-day remand after producing them before the court of Cox’s Bazar Senior Judicial Magistrate Court on Tuesday.
Earlier on Monday night, RAB detained the trio for interrogation.
The arrestees are assistant sub-inspector (ASI) Shahjahan, and constables Rajib and Abdullah, who were on duty at APBn’s Shamplapur check post in Teknaf, Cox’s Bazar on the day of the killing.
With this, So far 13 people have been arrested over Sinha’s murder.
Lt Col Ashik Billah, Director (media) of RAB confirmed the matter to journalists.
Earlier, ten people including seven policemen – OC Pradeep Kumar Das, Inspector Liakot, SI Nanda Dulal Raxit, constable Safanur Karim, constable Kamal Hossain, constable Abdullah Al Mamun and ASI Liton Mia – and three witnesses in a case filed by police including Mohammad Iyas, Nurul Amin and Nizam Uddin from Marishbunia village of Teknaf were arrested in connection with the killing.