Ramkumar, 25, a silver medallist in the 69kg category boxing at the 2013 Myanmar SEA Games was arrested in connection with a kidnapping case in Klang.
The 13 were: Muhamad Mustaqim Anas, 24; Mohd Hisham Mohd Daud,33; Muhammad Faizal Mahemod, 33; Mohd Basiran Mohd Bharuddin, 27; Ahmad Hanafi Ahmad @ Sufaat, 47; Bariq Ashlami Abdullah, 24; Sahrol Afindi Sahanudin, 25; Mohd Iszaruddin Ismail, 25; Mohd Rajis Abdul Rahim, 33; Mohd Zaki Shaari, 30; Noor Fadzlee Zizan, 24; Sophian Dahlan, 34; and Noridil Fitri Nordin, 31.
They were jointly charged with committing the offence at Cell 51, Level 2, Abadi Block 2 at the Sungai Buloh Prison near here, between 12.45pm to 1pm on April 16.
They were charged under Section 149 of the Penal Code read with Section 302, which carries the mandatory death sentence upon conviction.
The men nodded when the charge was read to them by a court interpreter. However, no pleas were recorded.
Magistrate Farah Azura Mohd Saad fixed May 26 for mention pending the post-mortem and chemist reports and DNA tests.
Deputy Public Prosecutor Nurulhuda Ramli appeared for the prosecution while all the accused were unrepresented.
Newspapers had earlier reported that a prison inmate was stabbed to death when a fight broke out between members of two gangs at the Sungai Buloh Prison.
Sungai Buloh police chief Supt Mohd Rozi Jidin reportedly said initial investigations found the victim was stabbed in the back with a sharp weapon.
-BERNAMA