Sylhet Metropolitan Magistrate Anwarul Haque remanded Amin in police custody on Sunday.
Police said Amin allegedly helped in carrying away Rajan’s body after the murder and had threatened Rajan’s father for having filed a case.
Investigation officer and Sylhet Detective Branch Inspector Suranjit Tarafder had sought a 10-day remand.
Amin, 35, was arrested in Sylhet’s Tukerbazar on Saturday afternoon.
His brother-in-law, Ali Haider, is also an accused in the murder case.
Rajan was tortured to death at Sylhet’s Kumargaon on July 8 on the suspicion of theft. The torturers had filmed the incident and posted it on a social networking site.
Haider, his brother Muhit Alam, Alam’s brother-in-law Ismail Hossain Abluchh, local watchman Moyna Mia, Dulal Mia and Nur Mia, who allegedly captured the torture, were also remanded.
Including them, 11 people have so far been arrested in connection with the murder.
Alam’s wife Lipi Begum is also among those arrested.