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The question

Layman here. This question was inspired by this question and random things I've heard/read over the years.

I'm quite confused by a concept that comes up again and again and which people seem to hold for self-evident. And that concept is that there is some evidence which a court will refuse to admit. And that confuses be because... well, there's evidence. It leads to the truth. Why aren't you taking it?!

It's very easy to come up with realistic examples where:

  • There is a piece of evidence which is clearly and irrefutably shows that a person did something very bad (say, murder)
  • This evidence is for whatever reason "not admissible" (say, it was obtained illegally)
  • And there is no other piece of evidence that would incriminate this person.

Does that mean that the perpetrator gets to go free? How can the court refuse to admit evidence, especially if it's the only useful evidence existing? And if yes, then why is this so and where is this practice useful?


Some examples from the top of my head

The example question above deals with unlawful searches. Imagine that a police officer decided to search a car (or an apartment) and forcefully did so against the protests of the owner (or maybe the owner wasn't even present). They thought they might find drugs or something, but instead they are surprised to discover a dead body, clearly murdered. So... now what? According to the above question, since the search was illegal, this is inadmissible evidence in the court. Does that mean that the owner of the car/apartment gets to go away scott-free? Do they launch a new investigation and try to find other evidence except the fact that it was inside the property of this guy here (and failing to do that, release them)? If the owner of the car/apartment says "I don't know what you're talking about, I last saw Jimmy here alive and well at the pub last night; I never seen his corpse before." - can they call him out on the obvious lie?

Or, another example. I don't know about USA, but here in Europe it's illegal to record someone's phone calls without a warrant (or something like that; it's serious). Any recordings obtained unlawfully will be inadmissible as evidence.

Let's now imagine that I've gone the full extra mile and have secretly bugged everything in my neighbour's house because I suspect (but have no evidence) that they murdered my child last month. I've got hidden cameras, microphones everywhere, etc. So one day I catch him talking to his spouse on the phone and mentioning the murder, admitting to doing it, and even telling where he buried the body.

Now I have evidence... or do I? I give the recording to the police, they search the indicated place and they do find the body, but since they cannot accept my recording as evidence... does that mean that my neighbour now has no consequences? Let's also suppose that no other evidence is found that would indicate his guilt (the guy was thorough). Obviously I'd get some grief for bugging my neighbour's house, but do I now also become the prime suspect in the murder of my own child? After all - the recording of my neighbour's confession "officially doesn't exist", and I'm the one who told the police where to dig, so...

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    Please add a jurisdiction as the answer can change dramatically without it.
    – hszmv
    Sep 7, 2022 at 10:55
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    @hszmv - I don't have one in mind, this seems to be a very common theme in all jurisdictions that I've heard of. OK, maybe in something like Sharia law (which is based on religious texts) this is different, I don't know. Can I say "any jurisdiction where this is a thing"?
    – Vilx-
    Sep 7, 2022 at 12:04
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    By the way, not all jurisdictions let courts refuse evidence. In Sweden fri bevisprövning (something like "free examination of evidence") applies: you can present any evidence you can get your hands on, but the court may not give it any particular value.
    – mystery
    Sep 7, 2022 at 17:22
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    @JamieB, ...doctrine of inevitable discovery applies there: if a legitimate investigation would have eventually gotten there via some means that doesn't involve cheating, evidence can find its way back in. Sep 7, 2022 at 20:06
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    This is much more prevalent in the US than in other parts of the world.... and the answers you have gotten so far are quite US-centric. Just saying, take this with a grain of salt.
    – Polygnome
    Sep 8, 2022 at 8:12

10 Answers 10

36

Different exclusionary rules have different reasons.

Hearsay is frequently inadmissible because it's less reliable for the court to hear Alice saying "Bob told me that Carol hit him" than to hear Bob saying "Carol hit me." Another even more critical problem with hearsay testimony is that the defense cannot cross examine the person who made the statement in court. If Bob is there, the defense can ask questions such as "where did Carol hit you" and "did Carol use her right or left hand" to clarify the testimony or call its veracity into question. Alice, not having been a direct witness to the act, will not be able to respond to many of these questions.

Evidence obtained in violation of a constitutional right is inadmissible because admitting it amounts to allowing police or prosecutors to violate people's constitutional rights in order to obtain convictions. Not only does an unconstitutional search itself violate the rights of the person being searched, but so does the use of evidence acquired in such a search. See Fruit of the poisonous tree at Wikipedia and the cases linked therein, especially Silverthorne Lumber Co. v. United States and Nardone v. United States.

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    Comments are not for extended discussion; this conversation has been moved to chat.
    – feetwet
    Sep 7, 2022 at 22:28
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    Would you consider adding the following: > Privileges are another reason that relevant information is excluded from court. The common law and legislatures have recognized that certain relationships require such a high guarantee of privacy that information exchanged in those relationships should not be compellable before a court. Examples are solicitor-client privilege, executive privilege, spousal privilege, and journalist-source privilege (a non-absolute statutory privilege in the Canada Evidence Act).
    – user46677
    Sep 8, 2022 at 21:11
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    Another issue with hearsay is that it doesn't come with the penalty of perjury. If Bob says to Alice "Carol hit me", and Carol did not in fact hit him, he can't be charged with perjury, because he didn't make the claim under oath, and Alice can't be charged with perjury, since her claim that Bob made the claim was in fact true. Sep 9, 2022 at 2:36
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You need to ask why evidence gets excluded. For example evidence that was obtained by a search without a proper warrant. That's not excluded to protect criminals, it's excluded so that law abiding citizens are protected from having their home or their car or their body searched by a police officer. So first we have a law: A police officer is not allowed to search your home without a search warrant.

But what if they do? As a society, we want to prevent it from happening, and you prevent it by having punishment. However, if you punish police officers directly, you have the problem that a police officer is with one foot in jail all the time, so nobody wants to be a police officer. If we had a law that they get punished if they search your home and nothing against you is found, that would give a police officer very good reason to fabricate evidence to find. So the punishment is something that (a) any police officer dislikes and (b) that makes searching your home without a warrant pointless: And disallowing any evidence from such a search is something that any police officer dislikes, and makes them look for legal ways to find the evidence.

Comments: "Trusting that the existing American systems for disciplining officers could reliably deter officers from violating citizens' right is also somewhat optimistic". Any search without warrant would end up in court, in front of a judge. Who would ask for the search warrant, there wouldn't be one, so the search was without warrant, so the police officer is in trouble. Now if you think police officers would come and search my home just to have an excuse to mess it up, that's outside this question.

Vilx: phoog explained the law. I tried to explain why the law is there and in that form and not another form.

All in all, it is a very simple rule (simple rules are easy to follow), it protects innocent people from searches without search warrant (because police officers would have zero motivation to perform such a search), and it doesn't protect people committing crimes much (because when a person has committed a crime, hopefully the police would be able to get a search warrant, while for a person not committing any crime this would be less likely).

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    I am asking why evidence gets excluded. It's literally there, in my question: And if yes, then why is this so and where is this practice useful? Anyways, I'm not sure I follow this part: However, if you punish police officers directly, you have the problem that a police officer is with one foot in jail all the time. Why so? If they search someone with a warrant, they are in the clear.
    – Vilx-
    Sep 7, 2022 at 13:28
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    Trusting that the existing American systems for disciplining officers could reliably deter officers from violating citizens' right is also somewhat optimistic. Sep 7, 2022 at 18:22
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    The line However, if you punish police officers directly, you have the problem that a police officer is with one foot in jail all the time is suggesting that if you punish officers directly for conducting an illegal search and seizure, it becomes in an officer's best interest to conduct no searches or seizures (and possibly avoid the profession entirely) rather than risk punishment for mistakenly believing a search is lawful. If they're insulated from direct consequences but risk their evidence being thrown out, they can safely conduct whatever they believe to be a legal search. Sep 7, 2022 at 20:42
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    @Vilx- A lot of what you just said is the idea behind qualified immunity; and the shooting scenarios you gave are an example of what's driving some jurisdictions to question whether LEOs should have qualified immunity. One thing that occurs to me is that there's a chain of people involved here; having illegal evidence be inadmissible frees you from figuring out who to punish (as opposed to having a LEO say their superior verbally ordered them to do it, etc) since it's in all of law enforcement's best interest that evidence be admissible. Sep 7, 2022 at 23:38
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    @Vilx- real police officers and departments are very much evaluated based on the number of fines, arrests and convictions they achieve. Sep 8, 2022 at 16:58
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TL;DR: The law against torture and unwarranted searches have the same base justification: to protect the guilty. Why protect the guilty? Because if the law doesn’t protect the guilty, it won’t protect the innocent. As proven by the fact that something other than the law was used to determine they were guilty.

Long version: Some “evidence” isn’t actually evidence. Hearsay is the prime example of that, and it is excluded because while it appears to be evidence it’s actually not. If Sally tells Jenny that she robbed the 7-11 the day before, that doesn’t even prove that Sally was in the same time zone as the 7-11 at that time, let alone that she actually robbed it.

Another example is confession under torture, is that evidence? The accused was burned until he said what he was told to say, that may or may not have lead to other physical evidence, but can you trust that evidence? Is it evidence against the accused, or evidence against the person that burned him until he said what they wanted him to say? Or was there someone else involved that told the torturer what to get the accused to say?

But you are probably thinking of the simple case of searching without a warrant, surely that is safe? Searching without a warrant is a crime, with multiple offenders, it is also a conspiracy to commit the crime. You want to trust the word of people who committed a crime and engaged in a conspiracy to commit a crime against a person to present evidence they supposedly found confirming the guilt of the person they are conspiring against?

So why not make it legal, then there’s no problem right? It’s not a crime, there is no conspiracy, everything is good, right? Except historically those in power have been quite willing to order their minions to make up evidence against those they deemed enemies, as well as having them tortured into confirming that the evidence was true. Even if we suppose we have a better class of bad Powers That Be nowadays, that wouldn’t be willing to torture people, expecting them to not make up evidence against people that they HONESTLY (but carelessly) believe are guilty is most certainly factually wrong, proven by various court cases where they did just that to convict people they thought were guilty.

Throwing out illegally obtained evidence is the least we can do, because it’s generally not practical to punish the criminal’s who illegally obtained evidence as they deserve. Why isn’t it practical? Because frequently it takes a law degree and several hours of study to come to the correct conclusion, and the cops don’t have that kind of time. Also, it’s hard to tell the difference between didn’t care and didn’t know. The appropriate punishment would be the same as the accused would face if convicted of the crime, and if you make it a capital offense to get it wrong, it’ll be a lot easier and safer for the cops to shoot someone they think is guilty in “self defense” than to try to collect the evidence.

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    And my answer is exactly the opposite: The laws are there to protect the innocent.
    – gnasher729
    Sep 8, 2022 at 13:55
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    @gnasher729: if they are there to protect the innocent, then it’s ok to ignore them when dealing with the guilty. And everyone is guilty once the red hot pincers come out.
    – jmoreno
    Sep 8, 2022 at 21:14
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    Everything has a cost. That's not something arbitrarily to be reduced or eliminated. It's something to be taken into account when choosing action or policy. If we choose not to accept protecting the guilty, then we do not get the benefit of protecting the innocent. And I am of course speaking in terms of actual guilt or innocence in this regard, as a moral question, which is certainly the correct framework for understanding how we arrived where we now are. You seem to be using the terms differently. Sep 9, 2022 at 0:37
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    And the innocent do need protection -- not particularly those whom authorities are sure are innocent, but rather those who are innocent despite being suspected, and those who are innocent but happen to catch the attention of an authority, and those who aren't especially suspected but happen to be in the wrong place at the wrong time. And that assuming only pure motives on the part of the government. Sep 9, 2022 at 0:48
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    @JohnBollinger I will add: those who are (according to fallible, flawed humans, some of whom are hired as police officers) of the 'wrong' skin color, genotype, culture, religious beliefs or lack thereof; wear the 'wrong' clothing, 'wrong' hair length / color / style, ... Sep 9, 2022 at 16:25
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The issue is that generally, evidence obtained without due process is inherently unreliable. For your first example, to legally get a warrant in many countries, you need to have to present a convincing argument that a crime was committed. In the case of searches, not needing to do so could easily allow for the planting of evidence on pretty much anyone. How could you know that the police officer hadn't knocked over a cyclist, thrown their body in the boot of the nearest person's car and "just happened upon it" later because they decided that the person might have drugs?

Unlike the example you give about police with guns making split second decisions, a search is a planned and coordinated act usually involving multiple people and other people not necessarily present may also be responsible for these actions (like a superior officer). As mentioned in another answer, to make sure justice is being served, it's also a better deterrent to enact a penalty that affects all parties and not just an individual or group of individuals.

With any evidence presented to a court, there has to be a level of trust that this evidence is legitimate. Obtaining it illegally undermines that trust because once someone has proven willing to break the rules to obtain it, how can you trust that they haven't broken the rules and invented it or tampered with it?

Your latter example is interesting because the difference here is that this evidence is submitted by a civilian. Depending on the circumstances, region and if there are checks you can make on the evidence's validity, it could still be deemed admissable. After all, if I were to rob a house and witness a murder, many countries would still allow me to take to the stand and give testimony (which is evidence). Me having committed a crime to see this doesn't change that. In the case of law enforcement recording people, the people retrieving and verifying its validity are the same, an obvious conflict of interest.

Either way, evidence not being admissable in a court of law wouldn't make you a suspect, it just means the police would have to find other evidence, and the location of a body might help provide enough so it would still be useful information for them.

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    – Community Bot
    Sep 8, 2022 at 12:32
  • This seems to be the first answer that addresses the examples in the question. +1
    – justhalf
    Sep 10, 2022 at 2:51
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that confuses be because... well, there's evidence. It leads to the truth. Why aren't you taking it?!

Firstly, because whether a piece of evidence actually leads to "the truth" is usually arguable. The parties will normally have different views on whether it does.

For example, someone saying something about what they saw/heard is evidence. But is the person to be believed? Are they available to repeat the evidence from the witness stand, or are only their words available (as heard/recorded by someone)?

And then, very importantly, the courts do not actually seek "the truth". It's a common misconception that they do. Instead, they resolve the dispute between the parties.

So, rules have been worked out over the centuries as to how disputes are to be resolved. These include rules of evidence.

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    What is truth is a philosical concept with thousands of years of critical thought behind it and no real widespread consensus.
    – Neil Meyer
    Sep 7, 2022 at 10:00
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    The courts can only ask the allowed evidence be put trough the reasonable doubt standard and hope that the truth will be served.
    – Neil Meyer
    Sep 7, 2022 at 10:01
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    OK, but how does this all lead to "this is a piece of evidence that we will not accept because it was obtained illegally"? What is the reasoning behind this? Note that I don't question the veracity of the evidence. I can totally understand not accepting unreliable evidence. I'm talking about the cases where the evidence can be verified to be true, and yet still rejected.
    – Vilx-
    Sep 7, 2022 at 12:19
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    @Vilx-, look up "qualified immunity". As implemented in practice, it provides police officers an extremely broad defense (considerably broader than theory might imply on account of second-order effects: an officer isn't considered personally liable unless they should have known violating someone's rights were illegal, and courts find that it would be illegal if there were a record of successful prosecutions, but because officers violating civilians' rights always get away with it on account of there not being precedent there often are no prior successful prosecutions to meet that standard). Sep 8, 2022 at 2:17
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    @CharlesDuffy just a nitpick: qualified immunity applies in the context of civil claims made against the officers by the rights holder. So rather than there needing to be a "successful prosecution" it should say "successful claims against officers on a nearly identical basis." There is also acknowledgment that some violations are so flagrant and obvious that there is no need for prior precedent squarely on point (Hope v. Pelzer (2002)).
    – user46677
    Sep 8, 2022 at 4:57
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Does that mean that the perpetrator gets to go free?

Quite possibly, depending on the case.

Why is this so and where is this practice useful?

At some point it was decided that it's better to let some guilty people go free than to allow violations of constitutional rights in order to get convictions.

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  • Mind you, the person doing the violation would also know full well that they would get punished for their transgression to the full extent of the law. Shouldn't that be enough to stop them?
    – Vilx-
    Sep 8, 2022 at 16:06
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    @Vilx- looking at the amount of inadmissible evidence that gets excluded on that basis, it does not.
    – Aubreal
    Sep 8, 2022 at 16:44
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How can a court refuse evidence? Because there are clear rules as to how evidence can be obtained and how they can be entered into a trial.

It is worth noting that concept of justice is not just who did the crime must do the time. Justice for the victim is just as important as justice for the accused.

If police obtain evidence illegaly then it is for the sake of justice that, that evidence is excluded.

If that means an otherwise slam-dunk case gets thrown out then that is inline with justice being served not against.

Poor policing is not the accused problem. Nor should the system allow police to do whatever they like.

The blackstone ratio, being a cornerstone of legal thought in much of the west says... "It is better that 10 guilty people go free than 1 innocent person suffer."

Our justice system is skewed to bring forth not guilty verdicts. As unpleasant as that view may be to victims of crimes. As disgusting it is when terrible crimes are not punished in a way that alleviates our need for revenge.

It is the system we have and a concept you will only truly appreciate when you get accused of a crime.

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    OK, but how does this all lead to "this is a piece of evidence that we will not accept because it was obtained illegally"? What is the reasoning behind this? How does this help not to falsely convict people?
    – Vilx-
    Sep 7, 2022 at 12:20
  • Read this. To put it simply the concept of guilt out of a legal pov is different than the collequil sense. Before I got myself legally educated on this site I thought the same way - law.stackexchange.com/questions/62104/…
    – Neil Meyer
    Sep 7, 2022 at 12:50
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    I read that link, but I still do not grasp the difference or how it applies here. Yes, people are not perfect and evidence is not perfect and wrong judgments do happen (guilty people are found not guilty and vice versa). And i also understand that the system is skewed towards not falsely finding one guilty. That is all fine. But how is dismissing some evidence (even if it can be demonstrated to be true beyond reasonable doubt) supposed to lead to less false convictions?
    – Vilx-
    Sep 7, 2022 at 13:19
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How can the court refuse to admit evidence, especially if it's the only useful evidence existing? And if yes, then why is this so and where is this practice useful?

The rules of evidence define what is and isn't legally evidence, and what is and isn't admissible. These rules vary by jurisdiction, and may differ in civil and criminal law. As underlined by phoog in their answer, you don't want to reward investigators who act above the law and violate your rights, and you don't want to give evidence credibility it has not earned.

Consider that in a jury trial, like criminal trials in the United States, the worst thing that can happen is that someone is wrongfully convicted because a jury was presented shaky evidence that influenced their judgement, even if they were told to ignore it. The second worst thing may be that the trial has to be redone because the jury's judgement was tainted by the evidence, making everybody lose precious time and money.

Conversely, in a trial by a professional judge, the judge knows the law and is better equipped to evaluate a piece of evidence. The risk of their judgment being influenced by wrongful evidence may be considered negligible since by definition a professional judge is trusted with their judgement and their ability to tell right from wrong, in a way individual jurors simply aren't.

This might explain why rules of evidence are much more stringent in the United States than in France, where illegally obtained evidence may be admitted. But even if admitted, you still have to show that the evidence is genuine, not tampered with, and actually shows the thing you say it shows, or else it has little value.

I give the recording to the police, they search the indicated place and they do find the body, but since they cannot accept my recording as evidence... does that mean that my neighbour now has no consequences?

The rules of evidence need not apply to a police investigation. If we presume your recording is inadmissible, it means it can't be brought to court. But the police isn't the judiciary (it is, in fact, the executive), and an investigation isn't a prosecution or defence.

Rules may vary, but generally inadmissible evidence can still be used in the course of an investigation. Suppose a police officer overheard someone talk about your neighbour and how they heard from someone that they buried a body in the forest. That would be woefully inadmissible evidence by itself (two words: objection, hearsay). However, it may give cause to the officer to grab a shovel and start digging.

If the police finds a body on the basis of your illegal recording, then they still find a body. The recording is essentially an anonymous tip, it can't be used in court, but the body you find thanks to it can be used, and you and your neighbour can definitely become a prime suspects in a homicide investigation.

In the unlikely event the investigation can't turn up any useful and admissible evidence and exhausts all possible avenues, then it would most likely be shelved until such time new evidence turns up. Without useable evidence, prosecution can't show guilt beyond a reasonable doubt, so there's no point in going forward.

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Your question invokes fairness of outcomes, i.e. you perceive the system as more fair if it is more accurate in determining guilt versus innocence. In other words, distributive justice.

Another concept is fairness of process or procedural justice, i.e. the system is fair if everybody has to play by the same rules. If obtaining a wiretap was illegal, then we should not allow any recording into the courtroom, whether the recording was made or not. We should enforce that the "no wiretap" rule is followed to keep the playing field level, even if someone did make a recording.

Similarly, it can be argued that people don't have "due process" or "equal protection under the law" if the prosecution gets to break the rules of the legal system against some defendants and not others.

Under procedural fairness, I think there is also less of an assumption of an objective truth about guilt versus innocence. If you instead think about guilt or innocence as simply an outcome of a two-sided contest, you may see the importance that the contest have fair and consistent rules for all participants.

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  • It's kind of weird to think of a lawsuit as a contest. This implies that whoever has the best lawyers will win. And hint: better lawyers are usually also more expensive, so the contest often becomes about who has deeper pockets and can afford better lawyers. Which... kinda feels like of the opposite of what law should be (fair and impartial to everyone)? Even though there are plenty of real-world examples of exactly this happening, I don't really think this is a "feature" of the system, but more like a glaring fault.
    – Vilx-
    Sep 10, 2022 at 23:27
  • @Vilx- it would more be the best combination of lawyer and actual evidence that wins. The best chess player can't win without pieces. One would hope that lawyer's ability matters less than the evidence, but I generally agree about the real-world pitfalls.
    – usul
    Sep 11, 2022 at 19:14
  • Of course, the same kinds of concerns can apply in distributive justice. In your question, if we admit illegal evidence, rich people are more able to break the rules (e.g. hire someone to make an illegal search that turns up evidence) or protect themselves from broken rules (e.g. use methods to avoid illegal wiretaps), so if we don't exclude illegally-obtained evidence, again depth of pockets comes into play.
    – usul
    Sep 11, 2022 at 19:18
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There are already plenty of other answers which address matters like why evidence might get thrown out, but I would like to point out that evidence that gets thrown out can still influence a trial. I raise this point because you exemplified a scenario wherein your child is murdered by a neighbor.

Specifically, witnesses cannot provide testimony that would contradict physical evidence that was prevented from being heard at trial because that would be perjury. For example, suppose a police officer conducted an unwarranted search of a drug dealer's car and found a kilogram of cocaine. Because the cocaine was found from a warrantless search, it will be excluded from trial.

If, for some reason, the prosecutor wants to proceed to trial they will do so without being able to present the kilogram of cocaine. But by the same note, the defense will not be able to put forth a witness who testifies that there were no drugs in the car at all at the time of the search because that would be perjury and an attorney who prompted a question to elicit that response could be guilty of suborning perjury.

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  • But how could you prove that it was perjury, if you cannot bring the cocaine in?
    – Vilx-
    Sep 9, 2022 at 8:59
  • @Vilx- the judge of the trial for the cocaine charge is aware of what evidence has and has not been admitted into evidence and the reasons for its exclusion. This would be handled in pre-trial motions which admit or exclude evidence. Testimony that is known to be perjury would need to be stricken from the record and could not be considered by the jury for the cocaine trial. Assuming a prosecutor wished to proceed on a charge of perjury, that would be a separate trial, and in that separate trial the kilo of cocaine's presence in the trunk could be admitted into evidence. Sep 11, 2022 at 0:19
  • @Vilx- to clarify, evidence that is excluded from a trial for Defendant #1 because it was obtained in a manner that impugns Defendant #1's rights is evidence that doesn't exist for the purpose of that trial. However, that evidence may still be admissible in another wholly separate trial relating to Defendant #2. After all, the evidence in Defendant #2's trial wasn't obtained in fashion that denied Defendant #2 their rights. Sep 11, 2022 at 0:21

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