Sometimes following the rules of due process of law and the rules of admissibility of evidence requires letting the bad guy go free.
In court, truth does not matter. In court what matters is what you can PROVE by admissible evidence. (Admissible means the court will allow the evidence to be part of what the judge and/or jury uses to make the decision.)
Some evidence is not admissible because allowing evidence gotten in certain ways causes bad behavior by the police.
Police generally can NOT take a person to jail because of a traffic ticket (or do much searching either). You may not remember when a few rural male cops strip searched pretty girls who got traffic tickets.
Allowing confessions without the Miranda warnings (You have the right to remain silent ...) does not stop the lying to suspects, but a wise suspect asks for his free attorney. (The number of unwise people never ceases to amaze me.)
It is VERY HARD to see someone you truly believe to be guilty to go free. Sometimes the desire to punish the ones you believe to be guilty causes worse wrongs. Police officers have been known to beat up suspects, to question children without a child's representative, to plant evidence, to forge evidence, to lie to judges, to break in without a warrant, to encourage a person to commit a crime.
Each time a court finds that evidence is inadmissible it is based on 800 years of legal thinking by the best legal minds of their time. Both sides are heard by higher and higher courts until the best of the best decide that admitting the evidence causes more harm than good.
The rules limiting admission of evidence are NOT STUPID RULES, they are the rules that are at the heart and soul of a free society. Ignoring these rules of evidence means ignoring all law from the Magna Carta to the US Constitution in 2010. The Magna Carta and the US Constitution are basic legal documents where man finally said, "People have rights and these rights are ...". These documents are living, growing, documents with all courts continuing to define and explain "due process of law" and admissibility of evidence.
Generally, we in the legal profession do not share our 'dirty laundry' with you. We whisper in hallways, and talk only with true friends. Eventually, it becomes so bad the new reporters hear about it. Then the higher courts MAY make a new rule. But BAD ACTIONS have to have a consistent pattern before higher courts find that evidence has become too tainted to admit into court.
Unless, of course, you think it is OK for the police to 'round up the usual suspects' or to arrest people and keep them in jail without trial. Oops, I guess some of you think you can make exceptions. I WARN YOU to be as careful about the exceptions as you are careful about the rules.
None of this is easy. Attorneys, judges, and citizens will ALL DISAGREE about the rules and exceptions as applied to any one case.
But sometimes, what happened was WRONG, a wrong easily understood by the general public. Than, it is, without doubt, a violation of due process.
Long and hard lessons have taught us that how we treat the least important among us is how we can expect to be treated, especially if we publicly disagree with the powerful.