Definition of ‘pervert justice’
To try to stop the police from learning the facts about a criminal case
She was convicted of perverting justice for lying to the police.
Merriam Webster
Pervert the course of justice law
To act illegally to avoid punishment or to get the wrong person punished
The two police officers were charged with perverting the course of justice by fabricating evidence in the trial.
Cambridge Dictionary
Idioms
Pervert the course of justice
(British English)
(North American English obstruct justice)
(law) to tell a lie or to do something in order to prevent the police, etc. from finding out the truth about a crime
pervert somebody/something to affect somebody in a way that makes them act or think in an unacceptable or immoral way
SYNONYM corrupt
Some people believe that television can pervert the minds of children.
Oxford Dictionary
OVERVIEW
perverting the course of justice
QUICK REFERENCE
Carrying out an act that tends or is intended to obstruct or defeat the administration of public justice. Common examples are inventing false evidence to mislead a court (in either civil or criminal proceedings) or an arbitration tribunal, making false statements to the police, stealing or destroying evidence, threatening witnesses, and attempting to influence jurors. The maximum penalty is life imprisonment and/or a fine. The common-law offence of perverting the course of justice overlaps with certain forms of contempt of court and with the separate offence of tampering with witnesses. It is not an offence, however, to offer money to someone to persuade him not to proceed with an action in the civil courts; nor is it an offence to offer to pay reasonable compensation to the victim of a crime, if he will agree not to take criminal proceedings (Criminal Law Act 1967 s 5(1). However, once he has made a statement to the police in connection with possible proceedings, it is an offence to attempt to induce him to withdraw or alter his statement.
Oxford Dictionary