The Jury System Is the Safeguard Here.
It is far from perfect, but better than trials by judges alone as happens in many other countries.
For example, according to this, in Canada, one no longer has the right to jury trial for offenses which can result in less than FIVE YEARS imprisonment.
http://en.wikipedia.org/wiki/Jury_trial
Jury trials were abolished by the government of India in 1960
Absence of juries in Israel
And, in places like Palestine, Somalia, Cuba, etc, there are no trials at all, just executions.