As another poster pointed out, it is that the purity of the criminal justice system is more important than any given case. In any case there is more than just

As another poster pointed out, it is that the purity of the criminal justice system is more important than any given case. In any case there is more than just the accused on trial. Always and ever the system is on trial as well. If it were not then there would be insufficient checks and balances. Most importantly, putting the system on trial routinely is necessary, because while one man (one murderer, one rapist, one thief) can do a considerable amount of harm to others and society if set free in error the system is capable of doing much, much more damage if it is allowed to become corrupt, abused, misused, etc. One serial killer might kill hundreds. A corrupt system can kill thousands, or millions.