Is it correlated? At the end of the day 12 randomly selected people from the population decide whether the person is guilty or not guilty.
How that system can be corrupted, even by the skills of persuasion, is beyond me. Some facts are simply facts and no gift of communication can change that.
Lawyers are not magicians. Lawyers can't by simple force of intellect persuade the jury to acquit someone when the fact clearly show to any impartial reasonable observer, as normally is the case with a jury of 12 people, that the person has committed the crime.
You might have a stronger argument in regards to how decisions are made as to which case is prosecuted, how much resources are allocated to gathering the facts to prosecute a case related to drugs as compared to a case related to financial fraud, but in my opinion, once the person charged is in court, I think there is no corruption at all.
The a large percentage, perhaps even a majority, of trials end in the striking of some sort of deal before the case ever goes in front of a jury. You'd better believe that the successful local lawyer who's the DA's golfing buddy gets better deals than some zit-faced public defender who just passed the bar exam. I know that sounds quaint, but it happens all the time in America, especially in small towns where the good ole boys club is still very much a going concern.
In the UK you get 33% off the sentence if you plead guilty at the first opportunity, i.e. at the police station or the first time you appear in court, 20% at the second opportunity, etc.
This is the system, and it isn't fair.
The outcome of a criminal trial being strongly correlated with your bank balance is pretty much the definition of an unfair legal system.