Say person A makes a police report, and person B is present to overhear the statement of A. The police knows the fact B overhears the statement of A.

A makes false statements (negligent, reckless, willful, doesn't matter).

B then makes a statement, the same false statement as A.

The police knows the two statements were false, but this is probably also irrelevant.

Is there U.S. common law name of the rule or principle to separate those making the statements? Is there a name for a prohibition to prevent this sort of "adjustment" or even unintentional, subconscious bias?

Is it regulated by statute in California?

What jurisprudence exist to mandate the proper police conduct or prohibit the contrary?

Some self-search:

To assert probable cause the police must be able to provide “"reliable information from a credible person” (Aguilar v. Texas (1964) 378 U.S. 108, 119)

The importance of credible witnesses shows in this case:

"Evidence can be "used to impeach" a witness even if the evidence is not itself admissible, even to impeach. For example, if Haws' notes record Elliott's hearsay reports of Dr. Brady's hearsay statements, then the notes themselves would not be admissible, even to impeach Dr. Brady. But if Dr. Brady's hearsay statements, reflected in the notes, contradict his in-court testimony, then the notes could be used to impeach Dr. Brady by leading the defense team to call Elliott to testify regarding Dr. Brady's prior inconsistent statements, which, as such, would not be hearsay." (Paradis v. Arave (9th Cir. 2001) 240 F.3d 1169, 1179)

On "mutual reinforcement of opinion":

"Furthermore, it appears the identification here was a product of "mutual reinforcement of opinion" among the witnesses ( Clemons v. United States (D.C. Cir. 1968) 408 F.2d 1230, 1241, 1245 fn. 16), and it is unclear from the record whether or not the girls could have independently identified the defendant. It is clear they did not do so. Furthermore, they were unable to do so at the ensuing lineup." (People v. Nation (1980) 26 Cal.3d 169, 180)

1 Answer 1



No law requires police to keep people apart when making statements. Doing so is good police practice. In some police organizations internal regulations or procedures may specify that officers should do so. But those are not laws. In some cases witnesses may have had a chance to confer and agree on a story before police arrive, the police cannot prevent that. The trier of fact can take into account that witnesses had a chanc to agree on a false story.

  • What about the idea of "reinforcement of opinion"? Or, even so, "mutual reinforcement of opinion"? Maybe there is rule to deny a search warrant affidavit when there is a factual finding by the court in such case Aug 1, 2022 at 13:24
  • @CarlySchillenhauser I am not aware of any such rule. If the issuing magistrate thinks the statements given to support a warrant are unreliable, s/he can decline to issue the warrant, that is a judgement call, not a matter o a rule. Aug 1, 2022 at 13:41
  • 1
    @CarlySchillenhauser a court can decline to issue a search warrant if it finds the affidavit to lack credibility. The court can make such a finding for any of several reasons, including for example if it learns that the police gave witnesses an opportunity to coordinate their stories. But, as this answer says, that doesn't mean that poor police practice is illegal; it just means that poor police practice can work against the efforts of police and prosecutors to pursue charges against someone.
    – phoog
    Aug 1, 2022 at 13:43
  • @CarlySchillenhauser consider the analogy of a police officer who renders some physical evidence useless by mishandling it. It's not necessarily illegal to do that; it just means that the evidence is no longer helpful to the prosecution. If the consistency of two witnesses' stories is held out as evidence of credibility, and then it comes out that they had several hours in private together before their first interview with the police, the consistency of their stories is no longer very useful evidence of credibility.
    – phoog
    Aug 1, 2022 at 13:48
  • @David Siegel /@phoog I added some self-research Aug 1, 2022 at 18:39

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