THE JUST SHOULD MAKE A PROPER INVESTIGATION
Na tena hoti dhammattho yen' attham sahasa naye
Yo ca attham anatthan ca ubho niccheyya pandito.
He is not just if he decides a case arbitrarily; the wise man should decide after considering both what is right and what is wrong. 
THE IMPARTIAL ARE CALLED THE TRUE JUSTICES
Asahasena dhammena samena nayati pare
Dhammassa gusto medhavi dhammattho' ti pavuccati.
The wise man who decides not arbitrarily, but in accordance with the law is one who safeguards the law;
he is called 'one who abides by the law' (dhammattha). 
One day, some bhikkhus were returning to the monastery after their almsround in Savatthi. While they took shelter in a hall of justice during a heavy shower of rain they saw some judges who were deciding their cases arbitrarily after having taken bribes. They reported the matter to the Buddha who said, 'Bhikkhus! If one is influenced by monetary considerations in deciding cases, he cannot be called a just judge who abides by the law. If one weighs the evidence intelligently and decides a case impartially, then he is to be called a just judge who abides by the law.'