Justice can mean different things to different people and different cultures and socieites. .
If the Maguindanao Massacre happened in a democratic country like Canada, the families of victims can file a class action suit or criminal charges against the accused in criminal courts.
If there are sufficient evidence, the accused are then arraigned in court to face charges and could face indictments on various counts of ...i.e first degree murder, sexual assault, assault with firearms and dangerous weapons, aggravated assault causing death, illegal confinement, etc.
The accused can either plead guilty or not guilty to the charges.
If the accused plead not guilty...then he/she/they can re-elect to be tried by a Judge alone or by the Jury (12 Jurors).
The jury is task to decide impartially based on evidence which proves beyond reasonable doubt that the accused is guilty or not.
Todate, I am not familiar with the Criminal Justice System in the Philippines. So, you asked where is justice in the Maguindanao Massacre? I must admit that it is difficult to say. Your answer is as good as mine.