Suppression of evidence

Suppression of evidence is a term used in the United States legal system to describe the lawful or unlawful act of preventing evidence from being shown in a trial. This could happen for several reasons. For example, if a judge believes that the evidence in question was obtained illegally, he can rule that it not be shown in court. It could also refer to a prosecutor improperly or intentionally hiding evidence that he or she is legally obligated to show the defense. In the latter case, this would be a violation of the 5th amendment to the United States Constitution. This can result in a mistrial in the latter case and/or the dismissal of the prosecutor.

Exceptions

If the discovery of an item(s) was obtained by illegal means, it may still be allowed into evidence under some circumstances. These exceptions include:

Inevitable discovery - if discovery of the evidence was inevitable via purely legal means
Independent source - if the discovery involved a combination of legal and illegal means, but the illegality was of marginal significance, such that the evidence could have been discovered based on the legal source alone
Standing - the violation affects the rights of someone other than the defendant, and the defendant does not have standing to complain
Good faith - the illegality is not the fault of the law enforcement officers who obtained the evidence, who did so pursuant to a facially valid warrant granted by a neutral and detached magistrate.
Attenuation - If the relationship between the illegality and the nature of the evidence obtained is reduced sufficiently for the evidence to be considered untainted (e.g., use of a booking photo from an unlawful arrest to identify the defendant in a lineup)

Evidence obtained as a result of Miranda violations is also subject to special analysis, depending on whether the statement is deemed voluntary or coerced, not merely whether police provided the appropriate warnings.

References

CPS in the uk suppress evidence http://stanw965.wix.com/misscarge