The criminal justice system is inherently unfair, for a lot of reasons, of which two of the most salient, are the fact that those with access to money and therefore a good attorney are going to have an entirely different justice experience than those that are impoverished; who because they often aren't able to make bail, are thereby typically incarcerated, pending their outcome, and therefore under intense pressure to make the best deal that they can, in order to resolve their outstanding charges. The other very important reason why our criminal justice system is so unfair is that an incredible amount of people that have been charged with some sort of crime, have been placed into their unenviable position by the testimony of a person or persons working as an informant, who themselves have often been unduly pressured into performing such, on behalf of the justice department.
It would be one thing if informants provided their information to government authorities, out of a sense of doing the right thing, that is, by doing their civic duty, so to speak; but in actuality, the vast majority of these informants, almost without exception, get into the business of informing, or snitching, in order to first, protect their own self, and secondly to gain something in return from governmental authorities. In other words, people that are caught in their own criminal activity, may find themselves being provided with a deal, that either reduces their sentence, substantially, or frees them from having to do time, or provides them with some sort of monetary compensation, when they agree to finger other "bad guys" for the expressed benefit of those justice department agents, whether these be police officers, or prosecution authorities.
As might be expected, though all that testify in a court of law, must testify under oath, it almost goes without saying, that those so testifying that have been offered a deal by the justice department, or by the police that serves to have reduced their own sentencing, or resulted in the dismissal of their charges, or has provided some sort of compensation to that informant, are going to testify in a manner that follows the script of what the prosecution authorities so desire, irrespective as to whether such is the truth, the whole truth, and nothing but the truth. Further to the whole truth, how is it therefore possible for those hearing that testimony to be receiving the whole truth, if the deal so structured for that informant, formal or not, is not fully divulged to those judging the reliability of that testimony?
Additionally, there is an inherent unfairness when the prosecution, for lack of a better word, is able to "bribe" informants to testify in a manner that benefits those informants, by providing them with a reduced sentence, reduced charges, or their freedom; whereas on the other hand, the Defense attorney, has no corresponding legal option or power to do the same sort of thing, indicating that if a given person is going to give false or misleading testimony, that the prosecution quite clearly provides a much better package deal for them.
The fact that so much of our criminal justice system activity, leans so heavily on informants of all stripes, of which, the deals so being structured for them, are typically done in a manner that is non-transparent, non-disclosed, coercive, and unfair, leads to the inevitable result that our justice so rendered is neither going to be impartial or fair.