Manoj, Mohit, Yashpal and Suraj, undergoing trial in criminal cases and having personal enmity with the victim, were identified as accused in the case, police sources said.
Prithvi's body was spotted by guards in the jail number 8 of the prison yesterday.
The accused inmates and the victim were lodged together in Rohini jail earlier and were shifted to Tihar recently.
Their enmity continued in Tihar also although they were kept in separate jails, said a police officer.
Prithvi was in jail in a murder case, committed in 2011. He was a resident of south Delhi's RK Puram locality.