The Rapid Acton Battalion (RAB) on Wednesday said the three men who were made witnesses in the Major (retd) Sinha Md Rashed Khan murder case filed by police were involved in incidents that led to the killing.
The three are Nurul Amin, Nizam Uddin and Md Ayas.
"The investigation officer determined their involvement in the murder. That is why he took them into custody," said Lt Col Ashique Billah, director of RAB legal and media wing.
"One of them is a community police member, another sought help for the robbery drama announced via the mosque's loudspeaker and the other continuously contacted Baharchhara police outpost Inspector Liakat Ali," he added.
Ten people – including seven policemen, Nurul Amin, Nizam Uddin and Md Ayas – were arrested in the case till Wednesday.
Meanwhile, a Cox's Bazar court on Wednesday placed seven arrestees, including four policemen, on a seven-day remand, each, over Sinha's murder.
Tamanna Farah, judge of Teknaf Upazila Judicial Magistrate Court, passed the order, said plaintiff's lawyer Advocate Mohammad Mostofa.
Those remanded are Assistant Sub-Inspector Liton Miah, three constables – Safanur Karim, Kamal Hossain and Abdullah Al Mamun – and the trio Nurul Amin, Nizam Uddin and Md Ayas.
The others accused in the case are Teknaf Police Station's suspended Officer-in-Charge (OC) Pradeep Kumar Das, Baharchhara police outpost Inspector Liakat Ali and Sub-Inspector Nanda Dulal Rakkhit.
The court earlier issued arrest warrants for Tutul and Md Mustafa, who were accused in the case filed by Sinha's sister Sharmin Shahriar Ferdous.
The investigating agency said they would also quiz Sinha's co-travellers Sifat and Shipra very soon.
"The investigation officer will interrogate them by Friday. On Thursday, the trio Nurul Amin, Nizam Uddin and Md Ayas will be taken into remand custody," Lt Col Ashique said.
On August 5, Sharmin filed a case with the Teknaf Upazila Judicial Magistrate Court accusing OC Pradeep and Inspector Liakat, among nine policemen, of the killing of his brother.
The following day, OC Pradeep surrendered before the court.
On August 11, RAB detained the trio Nurul Amin, Nizam Uddin and Md Ayas in Marishbunia area under Baharchhara of Teknaf in connection with the murder.
On the night of July 31, Sinha was killed in police firing on Marine Drive in Cox's Bazar.