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DNA - A Prosecutor’s Practice Notebook Inventory


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National Institute of Justice (NIJ) (see reuse policy).

The defense may assert the DNA typing result is not reliable due to possible contamination. First, the prosecution should deconstruct the defense challenge to isolate at what stage(s) the defense is arguing the contamination occurred: before or during collection, during transport and impounding, or after arrival in the DNA lab. Second, the state's DNA analyst should describe the rigorous procedures and protocols that were followed; inspection of evidence, packaging and seals; security procedures, chain of custody documentation, and quality assurance protocols. Third, the state's DNA analyst should explain what exactly contamination means and that if it occurred, it would result in a mixture which would be detected and reported during testing. Fourth, and most important, the prosecutor should have the DNA analyst explain that contamination can never transform one person's DNA into the DNA of someone else.

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