Contamination of Biological Evidence
DNA can be transferred to evidence directly or indirectly. This exchange of information between objects is based on the Locard Exchange Principle. The Locard Exchange Principle states that information is exchanged whenever two items come into contact with each other (Houck and Siegel 54). The direct transfer of DNA can be described as DNA that is “transferred from a source to a location with no intermediaries” (Houck and Siegel 55). The indirect transfer of DNA “involves one or more intermediate objects” (Houck and Siegel 55). Therefore, DNA is transferred from its source to an object of direct contact and the object comes in contact with another object, indirectly transferring the DNA. When this principle …show more content…
There are three types of biological material contamination. They are self-contamination, cross-contamination and secondary contamination (“Avoiding DNA” 1). Self-contamination occurs “when the investigator or examiner contaminates the scene and/or evidence with his or her own DNA” (“Avoiding DNA” 1). Cross-contamination takes place “when the investigator or examiner contaminates a scene and/or evidence from another scene and/or evidence (“Avoiding DNA” 1). “Secondary contamination is when the investigator or examiner inadvertently contaminates a scene and/or evidence with DNA from an intermediate object” (“Avoiding DNA” 1). “This can happen from touching pens, cameras, or other objects that bear the DNA or the investigator or examiner or of the victim or perpetrator” (“Avoiding DNA” 1). “Based on the Locard’s Principle, every contact produces some level of exchange, including contamination” (Houck and Siegel …show more content…
Dr. Jeffreys used the DNA fingerprinting technique that he had developed years earlier to crack the Colin Pitchfork case. In this case, “two 15-year-old girls by the names of Lynda Mann and Dawn Ashworth, were sexually assaulted and brutally murdered in close proximity to each other” (Buckleton et al. 1). “ In 1983, the 5 feet 2 inches, 112 pound body of Lynda Mann was discovered on a frosty lawn by the Black Pad footpath in the ancient village of Narborough in Leicestershire, England” (Buckleton et al. 1). She was undressed from the waist down and had blood exiting her body from her nose (Buckleton et al. 1). “In 1986, the body of Dawn Ashworth was discovered in the same village on Ten Pound Lane, not far from where Lynda Mann was found” (Buckleton et al. 1). Similarities in the crime, led police to believe that the same person had committed the murders (Butler 3). A local man came forth and confessed to killing one of the girls. When his blood was collected and compared to semen recovered from both crime scenes, his DNA did not match evidence from either crime (Butler 3). However, the DNA analysis of the semen present on vaginal swabs from the two girls did suggest that the same person had murdered both girls (Buckleton et al.
DNA can be transferred to evidence directly or indirectly. This exchange of information between objects is based on the Locard Exchange Principle. The Locard Exchange Principle states that information is exchanged whenever two items come into contact with each other (Houck and Siegel 54). The direct transfer of DNA can be described as DNA that is “transferred from a source to a location with no intermediaries” (Houck and Siegel 55). The indirect transfer of DNA “involves one or more intermediate objects” (Houck and Siegel 55). Therefore, DNA is transferred from its source to an object of direct contact and the object comes in contact with another object, indirectly transferring the DNA. When this principle …show more content…
There are three types of biological material contamination. They are self-contamination, cross-contamination and secondary contamination (“Avoiding DNA” 1). Self-contamination occurs “when the investigator or examiner contaminates the scene and/or evidence with his or her own DNA” (“Avoiding DNA” 1). Cross-contamination takes place “when the investigator or examiner contaminates a scene and/or evidence from another scene and/or evidence (“Avoiding DNA” 1). “Secondary contamination is when the investigator or examiner inadvertently contaminates a scene and/or evidence with DNA from an intermediate object” (“Avoiding DNA” 1). “This can happen from touching pens, cameras, or other objects that bear the DNA or the investigator or examiner or of the victim or perpetrator” (“Avoiding DNA” 1). “Based on the Locard’s Principle, every contact produces some level of exchange, including contamination” (Houck and Siegel …show more content…
Dr. Jeffreys used the DNA fingerprinting technique that he had developed years earlier to crack the Colin Pitchfork case. In this case, “two 15-year-old girls by the names of Lynda Mann and Dawn Ashworth, were sexually assaulted and brutally murdered in close proximity to each other” (Buckleton et al. 1). “ In 1983, the 5 feet 2 inches, 112 pound body of Lynda Mann was discovered on a frosty lawn by the Black Pad footpath in the ancient village of Narborough in Leicestershire, England” (Buckleton et al. 1). She was undressed from the waist down and had blood exiting her body from her nose (Buckleton et al. 1). “In 1986, the body of Dawn Ashworth was discovered in the same village on Ten Pound Lane, not far from where Lynda Mann was found” (Buckleton et al. 1). Similarities in the crime, led police to believe that the same person had committed the murders (Butler 3). A local man came forth and confessed to killing one of the girls. When his blood was collected and compared to semen recovered from both crime scenes, his DNA did not match evidence from either crime (Butler 3). However, the DNA analysis of the semen present on vaginal swabs from the two girls did suggest that the same person had murdered both girls (Buckleton et al.