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So chain of custody is obviously important, but why?

I have seen many articles referring to drugs and one where the murder weapon was handled without gloves. But what about other types of evidence being mishandled.

For example if a weapon believed used in a crime was in evidence and it was revealed at the time it was taken and stored before forensics in a evidence room that was unsecured, unguarded and other evidence was definitively tampered with. Would that mean the evidence regardless of the follow on forensics has a broken chain of custody? i.e. that department mishandled evidence in general as a practice and that resulted in a blanket dismissal for the time period. Due to bad paperwork practices the case for that evidence was filed (The evidence was sent somewhere else for forensic testing and the paper trail started there). The question is basically if evidence was mishandled, regardless of the evidence type, is that a broken chain of custody and if so does that mean the evidence will be excluded?

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Physical evidence must be authenticated to be admissible as evidence in court. In other words, the person seeking to introduce it as evidence must show that it is what it claims to be by some means (there are many legitimate ways to authenticate evidence).

A chain of custody is used to authenticate physical evidence.

Even if physical evidence can be authenticated sufficiently to be admissible as evidence, evidence that there was a break in a chain of custody could create a reasonable doubt that physical evidence which is key to obtaining a conviction is really evidence that was collected, for example, from a particular crime scene at a particular time.

This doubt could provide a basis for an acquittal of a defendant in a criminal trial if that piece of evidence was an important part of the case to show that the defendant was guilty.

  • follow up, so if the prosecutor stopped the investigation into the police mishandling evidence. the initial report was evidence bags not labelled, money missing and evidence bag torn open with content spilled out. IS there a legal dilemma for the prosecutor using that evidence since the investigation was not completed and no one can say their was no tampering? outside of any specific case just in general. – Danial Oct 6 '17 at 18:08
  • Upon a motion in limine, the judge would have to determine as a matter of law that such tainted evidence remains somehow relevant and thus admissible to the extent it can be authenticated. – Upnorth Oct 7 '17 at 3:03
  • @Danial The prosecutor would have a legal duty to disclose those facts to the defense (probably even if the evidence was not actually used). This would make the case much weaker. But, testimony from witnesses who was the untampered evidence could come in with the evidence of tampering offering to impeach it, and if the physical evidence was distinctive enough it could probably be admitted into evidence even absent a good chain of custody although the lack of chain of custody would undermine its weight. – ohwilleke Oct 9 '17 at 20:14
  • @Upnorth The relevance of the evidence isn't really affected by the lack of a chain of custody, just the ability of the prosecution to authenticate it. And even if it isn't admissible to prove everything it was originally offered for, it would probably be admissible to prove something it was originally offered for. For example, in a larceny case, it might be offered to prove larceny but the case that the larceny was in excess of $X to get an enhanced sentence might be impaired (although evidence from testimony of someone who counted it pre-tampering would still be admissible). – ohwilleke Oct 9 '17 at 20:17
  • @ohwilleke Sorry, I was mis-remembering the objection to raise when the person testifying as to chain of custody cannot actually show that the evidence presented is the same evidence as collected or analyzed at the crime scene or arising from the injury or damage being claimed. I suppose it would be ruled "immaterial" to the case, were it not properly linked to some fact to be proven. E.g., "Oops. Wrong lab results." – Upnorth Oct 10 '17 at 21:28

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