Reference samples presentation


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Reference samples presentation

  1. 1. TRACE EVIDENCEObtaining Standard/Reference Samples
  2. 2. Obtain Standard ReferenceSample The examination of evidence, whether soil,blood, glass, hair, fibers, and so on, oftenrequires comparison with a knowstandard/reference sample. Although mostinvestigators have little difficulty recognizingand collecting relevant crime scene evidence,few seem aware of the necessity andimportance of providing the crime lab with athorough sampling of standard/referencematerials. Such materials may be obtainedfrom the victim, suspect, or other knownsources.
  3. 3. Obtain Standard ReferenceSample Example: If we are investigating a hit-and-runincident, we would have to recover a “paintstandard” from the suspect vehicle tocompare to any paint evidence removedfrom the victim or victim’s vehicle. Thiswill permit its comparison to paintrecovered at the scene.
  4. 4. Obtain Standard ReferenceSample The presence of standard samples greatlyfacilitates the work of the forensic scientist.For example, hair found at a crime scene willbe of optimum value only when compared tohair standards removed from the suspect andvictim. Likewise, bloodstained evidence mustbe accompanied by a whole blood or buccalswab standard/reference sample obtainedfrom all crime-scene participants. The qualityand quantity of standard/reference specimensmust be treated with equal care.
  5. 5. Obtain Standard ReferenceSample FROM THIS POINT ON, IN THIS CLASS WEWILL REFER TO STANDARD/REFERENCESAMPLES AS:STANDARDSWhen I refer to “standards” – know that I am talkingabout standard/reference samples.
  6. 6. Obtain Standard ReferenceSample . Some types of evidence must be accompanied bythe collection of substrate controls. These arematerials close to areas where physical evidencehas been deposited. For example, substratecontrols are normally collected at arson scenes. Ifan investigator suspects that a particular surfacehas been exposed to gasoline or some otheraccelerant, the investigator should also collect apiece of the same surface material that is believednot to have been exposed to the accelerant.
  7. 7.  At the laboratory, the substrate control is tested toensure that the surface on which the accelerantwas deposited does not interfere with testingprocedures. Another common example of asubstrate control is a material on which abloodstain has been deposited. Unstained areasclose to the stain may be sampled to determinewhether this material can interfere with theinterpretation of laboratory results. Thoroughcollection and proper packaging ofstandard/reference specimens and substratecontrols are the mark of a skilled investigator.
  8. 8.  Evidence is usually submitted to the laboratoryeither by personal delivery or by mailshipment. The method of transmittal isdetermined by the distance the submittingagency must travel to the laboratory and theurgency of the case. If the evidence isdelivered personally, the deliverer should befamiliar with the case, to facilitate anydiscussions between laboratory personnel andthe deliverer concerning specific aspects ofthe case.
  9. 9.  If desired, most evidence can be convenientlyshipped by mail. However, postal regulationsrestrict the shipment of certain chemicals andlive ammunition and prohibit the mailing ofexplosives. In such situations, the laboratorymust be consulted to determine the dispositionof these substances. Care must also beexercised in the packaging of evidence inorder to prevent breakage or other accidentaldestruction while it is in transit to thelaboratory.
  10. 10.  Most laboratories require that an evidencesubmission form accompany all evidencesubmitted.
  11. 11.  An evidence submission form must beproperly completed. Its information will enablethe laboratory analyst to make an intelligentand complete examination of the evidence.Particular attention should be paid to providingthe laboratory with a brief description of thecase history. This information will allow theexaminer to analyze the specimens in a logicalsequence and make the proper comparisons,and it will also facilitate the search for tracequantities of evidence.
  12. 12.  The particular kind of examination requested foreach type of evidence should be delineated.However, the analyst will not be bound to adherestrictly to the specific tests requested by theinvestigator. During the examination newevidence my be uncovered, and as a result thecomplexity of the case may change. Furthermore,the analyst may find the initial requestsincomplete or not totally relevant to the case.Finally, a list of items submitted for examinationmust be included on the evidence submissionform. Each item is to be packaged separately andassigned a number or letter, which should belisted in an orderly and logical sequence on theform.
  13. 13. Richard Safferstein, Copyright © 2011 Pearson Education, Inc.,publishing as Pearson Prentice Hall, Upper Saddle River, NewJersey 07458.Notes from this power point are from Chapter 2 inthe textbook.