In The Crucible, in examining Reverend Parris, what evidence is there that justice didn’t prevail?

There are a couple of points to make here.  The first
would be that Parris is evidence that justice does not prevail because he is empowered. 
The fact that someone like him would be in the position of power is representative that
justice is not present.  Parris' insecurities, his coveting of power and control, as
well as the manipulative manner in which he uses religion are all representative of how
injustice is present if someone like him holds power.  Additionally, Parris' role during
the trials also feeds the idea that justice did not prevail.  Parris' pressures on
Danforth and the entire court proceedings is representative of a lack of justice.  His
pointed attacks on Proctor, seeking to pervert the court process to remedy his own
personal animosity, is also representative of how justice does not
prevail.

On another level, though, one could argue that
post- trial, justice does prevail with what happens to Parris.  It is evident in Act IV
that Parris' credibility with the judges is in doubt.  When he confesses that Abigail
has stolen his money and fled, that he is the source of death threats, and that he is
working on a "deal" to use Hale to secure confessions, it brings some level of doubt to
his position.  This also helps to show him as fraudulent, confirmed by the ending.  In
the last section of the play entitled, "Echoes Down the Corridor," the ending of Parris
does reflect that justice might have very well prevailed in the long
term:

Not long
after the fever died, Parris was voted from office, walked out on the highroad, and was
never heard from again.

For
someone that sought to be the center of everyone's attention, such an ending might be
just in its own right.