The trio Md Nurul Amin, Md Nezamuddin and Mohammad Ayaz were earlier put on remand on August 20.
The court on Monday placed each of seven accused including Officer-in-Charge of Teknaf Police Station Pradeep Kumar Das and Inspector Liakat, on four-day remand in the murder case.
The authorities on August 2, suspended 21 police officials, including the in-charge of Baharchhara police outpost, in connection with the killing.
Also read: Major (retd) Sinha murder: Accused put on further 4 days of remand
Major (retd) Sinha was killed in police firing at Baharchhara police check-post on July 31.
Sharmin Shahriar Ferdous, elder sister of Sinha, filed the case at Teknaf Senior Judicial Magistrate Court on August 5.
Also read: Major (retd) Sinha: Rab simulates killing incident with Pradeep, Liakat