What is the most important component of criminal justice system?I want the facts

There is no way to give you a factual answer to this question as it is a matter of opinion.

You could argue that juries are the most important component of the criminal justice system in the United States.  They are guaranteed by the Constitution and are the ones who determine guilt or innocence.

On the other hand, the vast majority of cases never go to trial because of plea bargains.  Because of this, you can argue that the prosecutors are the most important component because they are the ones who determine what plea deals will be offerred.