The answer is "prosecutors and defense attorneys".
To understand the major adversary actors we need to look at the definition of the criminal justice system. This is a progression of government offices and organizations whose objective is to distinguish and get the offenders and to deliver various types of penalties on them. Although there are many actors involved in this system like the police, arraignment and safeguard legal counselors, the courts and jails but the main are prosecutors and defense attorneys who play the major role in getting a criminal to get punished or otherwise.