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Principles of Forensic DNA for Officers of the Court


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Image of gloved hands holding a knife, collecting fingerprint, and collecting blood sample
National Institute of Justice (NIJ) (see reuse policy).

Biological material can be collected by taking the whole item, such as a pair of blue jeans or a knife, or by taking a representative sample of the item. A representative sample can be obtained by lifting, cutting, swabbing, or scraping.

Liquid samples can be collected by soaking up the sample with cotton-tipped swabs or gauze patches or through the use of a pipette.

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