In academia, there is an important distinction between exploratory analyses of data and confirmatory analyses. Careers have been ruined by researchers passing off the one as the other.

Since the gathering and introduction of evidence in legal proceedings is quite similar to the procedure in scientific circles, I was wondering if there are rules and procedures to safeguard against potential abuse (deliberate or accidental) of exploratory evidence.

A simple legal analogue of the case above might be, for example: Alice is picked up due to a separate investigation of her drug dealer whose phone contained drug-related texts to Alice. Her phone is confiscated, and its contents dredged for signs of anything and everything. The phone is found to contain illegal pornographic content. Questioning of friends and relatives reveal that they have a suspicion that Alice might be involved in the creation of illegal pornographic content. Contrast this with Bob, whose friends and relatives approach police with a suspicion that Bob might be involved in the creation of illegal pornographic content. Bob is arrested and his phone is searched for the illegal content hypothesized by his friends and family, which is found to reside on Bob's phone. In both scenarios, the evidence against Alice and Bob is ostensibly identical with the single exception that the evidence against Bob is confirmatory. Thus, although the situation looks grim for both, since the evidence against Bob is confirmatory, it might be considered stronger.

Would anyone be inclined to press such a distinction in court proceedings?

  • I think court proceedings would center around the legality of searching somebody's phone stemming from a jaywalking charge. I know that isn't what you are asking though... What country are you asking about? I can see something like that being legal in China, but not in the US... – Ron Beyer Feb 13 '19 at 20:45
  • Sorry, as I am not a legal scholar, I am unfamiliar with existing rules of evidence. I will edit the question to suggest a charge that would warrant a phone search. – Him Feb 13 '19 at 21:04
  • Is a succinct version of the question - Is evidence of crime A obtained in a legal search regarding crime A any stronger than evidence of crime B inadvertently obtained in a legal search regarding crime A? – George White Feb 13 '19 at 21:34
  • @Scott, your assumption that strength of evidence relates to the rationale for asking the question is not a fact, it's an ideological stance taken by some but not all philosophers of science. I think that kind of issue is best pursued on Philosophy SE. – user6726 Feb 14 '19 at 1:43
  • 2
    @Scott, there is an impenetrable procedural wall: illegally-obtained evidence is not admissible. Not just "given less cred", but forbidden. – user6726 Feb 14 '19 at 21:18

In US law, there was, as far as the question indicates, no probable cause to search her phone at all, Therefore (unless there is some cause not mentioned in the question), any such search is illegal, and any evidence found in such a search, or that is found as an indirect result of such a search (pointers toward it are found in the search, and followed) would not be admissible in any criminal case against Alice.

In the case of Bob, if his friends and family approach the police or other authority with

a vague suspicion that Bob might be involved in the creation of illegal content

That will probably not constitute probable cause for an arrest of Bob or a search warrant for his phone. Unless the accusation does prove to constitute probable cause, any evidence found during such a search would not be admissible against Bob in a criminal case.

In practice, most US police would not undertake either search without better evidence than is described in the question. But some police will overstep the lines, which is what the US exclusionary rule is for.

Legal procedure does not as far as I know make a distinction between "exploratory" and "confirmatory" evidence. Instead, evidence is either admissible or not. The rules for when evidence is admissible are quite complex, and vary by jurisdiction. Some of them are more traditional than logical, and some of them are addressed to particular problems that have arisen in particular circumstances.

But the US Fourth Amendment protections against unreasonable searches, and the requirement of probable cause before search or arrest warrants are issued, serves some of the same purpose.

Other countries have different rules, but many of them restrict the authorities to some extent from making arbitrary searches with no initial evidence.

Response to the Revised Question

As the question has been edited, there seems to be fairly clear probable cause to search Alice's phone, and if clear evidence of "illegal pornographic content" presumably actually child pornography, as no other kind is illegal simply to posses) is found, she can be brought to trial and perhaps convicted. The mere "suspicion" of Alice's "friends and relatives" would add little and mi8ght well not even be admissible. The facts, if any, on which those suspicions are based might be admissible, one cannot tell from the summary in the question.

The case against Bob, however, remains weak. Indeed there still seems to be no probable cause either to arrest Bob nor to se3arch his phone, and the results of any search that was done would not be admissible. Probably none would be done without more evidence.

The OP wrote:

Thus, although the situation looks grim for both, since the evidence against Bob is confirmatory, it might be considered stronger.

Not so, the case against Bob is weaker, indeed so weak that an arrest would be unlikely, and if one were made, the case would likely be dismissed before going to trial, assuming no more evidence than was included inn the question. The evidence prior to the search seems to consist only of vague suspicion not supported by any actual evidence, and so there is nothing to confirm, and no valid search would occur.

That suspicion of Bob came before the search, and the search is thus "confirmatory" is not relevant. The question is, what evidence against each defendant is admissible, and does the totality of the admissible evidence amount to "proof beyond a reasonable doubt" no matter what order it was discovered in, or what idea was in the minds of the investigators, provided that they were acting lawfully so that their findings are admissible.


There is no distinction between exploratory and confirmatory analysis in law. Assume that Alice is suspected of being a child pornographer (based on clear statements to that effect by multiple parties) and a warrant is issued to allow exhaustively searching her cell phone (the search has to be legal in the first place). The cellphone contains damning evidence of her crimes: on that basis she could be convicted. Now assume that someone says "I think Alice might be up to something shady": whether or not she is ticketed for jaywalking, there is not a reasonable suspicion that a crime was committed. Therefore no warrant will be issued, and no search is legal.

The "exploratory" part basically does not exist under the law. You cannot just explore, you need to already have confirmation.

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