People describe a trial as a show trial if they believe that the trial is unfair and is held for political reasons rather than in order to find out the truth.
[disapproval]
...the show trials of political dissidents. [+ of]
show trial in British English
noun
a trial conducted primarily to make a particular impression on the public or on other nations, esp one that demonstrates the power of the state over the individual
show trial in American English
a trial, widely publicized and seemingly open and fair, of a person regarded as a political subversive or ideological dissident, in which a verdict of guilty is assured by means of false evidence, a forced confession, etc.
Examples of 'show trial' in a sentence
show trial
Many regarded the court martial as a show trial designed to make British justice look effective.
Times, Sunday Times (2006)
It must deliver a fair trial, not a show trial, and one that does not stretch out to the crack of doom.