FBI Handbook of Crime Scene Forensics Read Online Free Page B

DNA. Consequently, mtDNA is not appropriate for evidence containing possible mixed sources of DNA such as semen stains from sexual assaults .
    Mitochondrial DNA analysis generally will not be performed on bloodstains unless the victim’s reference samples are not available or other appropriate reference samples are unavailable for nDNA analysis. For example, a kidnapping victim is missing, but a bloodstain is found in the suspect’s vehicle and only a maternal relative’s (e.g., mother, sibling) reference sample is available for the victim. In that case, mtDNA analysis could be conducted using a portion of the vehicle bloodstain, the maternal relative’s reference sample, and the suspect’s known sample.
    Mitochondrial DNA Analysis of Hair Evidence
    Mitochondrial DNA analysis should be performed on probative hair samples only if they are deemed unsuitable for nDNA analysis . Only those hairs having greatest probative value should be subjected to mtDNA analysis. If several similar probative hair specimens are submitted from one source of evidence, mtDNA analysis should be performed on only 1-2 hairs. For example, if 10 hairs collected from a victim’s body are microscopically associated with the suspect, no more than 2 hairs will be analyzed.
    Submission guidelines for mtDNA cases must include the following points for hair evidence:
Known victim hair samples (of all types) must be submitted to determine whether evidence hairs are similar or dissimilar to the victim’s hair.
If evidence includes specimens dissimilar to the victim, known suspect hair samples (of all types) should be obtained.
    Mitochondrial DNA analysis generally will be performed on all probative microscopic hair associations. In addition, the following types of hairs are considered for mtDNA analysis, if probative:
Hairs that exhibit “microscopic similarities and slight differences” (e.g., because of prolonged time between the crime and collection of reference samples, environmental or artificial changes to hair, or the suitability of reference samples or questioned hair).
Hairs that are not suitable for microscopic comparison purposes (e.g., body-area hairs, hair fragments, or any other factor that eliminates the possibility of performing a comparison). In such cases, however, the hair must be probative (e.g., apparent foreign hair in the pubic-hair combing of the victim).
Hairs that are suitable for microscopic comparison purposes but, for valid reasons, are not suitable to compare with the pertinent reference sample (e.g., hair deposited 10 years prior to the collection of the reference hair sample, reference sample is from an individual whose hair is artificially treated after the crime date). Regardless, the hair must be probative.
    Unidentified Human Remains
    Prior to mtDNA analysis, bone or teeth specimens should be examined by a forensic anthropologist or odontologist or a similarly qualified individual. Submissions of such items should be accompanied by a written report that verifies human origin by a qualified expert.
    Documenting, Collecting, Packaging, and Preserving DNA Evidence
    If DNA evidence is not properly documented, collected, packaged, and preserved, it will not meet the legal and scientific requirements for admissibility in a court of law.
If DNA evidence is not properly documented, its origin can be questioned.
If it is not properly collected, biological activity can be lost.
If it is not properly packaged, contamination can occur.
If it is not properly preserved, decomposition and deterioration can occur.
    When DNA evidence is transferred by direct or secondary (indirect) means, it remains on surfaces by absorption or adherence. In general, liquid biological evidence is absorbed into surfaces, and solid biological evidence adheres to surfaces. Collecting, packaging, and preserving DNA evidence depends on the liquid or solid state and the condition of the evidence.
    The more evidence retains its original integrity until it