Real Dictionary

show trial
countable noun: 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.

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.
noun: the public trial of a political offender conducted chiefly for propagandistic purposes, as to suppress further dissent against the government by making an example of the accused

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