Investigating CSI – Background material Table of Contents I ...

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I. OVERVIEW OF FORENSIC SCIENCE DNA EVIDENCE The work of the forensic scientist: IBMS West of Scotland Branch Meeting A well-attended IBMS West of Scotland branch meeting in early November saw Marie Campbell from Strathclyde Police forensic science department give a fascinating overview of the work of a forensic scientist. Her first point was to explain the difference between a forensic scientist and a forensic pathologist - the latter deals with autopsies while a forensic scientist deals with the scene of crime, evidence investigation and DNA testing. Forensic science divides into forensic chemistry and forensic biology. Forensic chemistry deals with drug testing, marks and unique striations on tools used in crimes such as burglary, footwear marks, fire scenes, firearms and shooting incidents, forged documents and handwriting, threatening letters or money. Drug testing is the perhaps the busiest role with thousands of cases processed every year. Fire debris is sifted through to find small pieces of evidence that would suggest a deliberate cause. The way a fire 'naturally' takes hold in a room indicates whether it was started deliberately but evidence can still be hard to find when it is covered by debris or a collapsed ceiling. Physical chemistry looks at footwear comparison and gelatine lifting off a suspect's shoes. Footwear comparison involves the electrostatic lifting of footwear if a burglar has stood, for example, on a newspaper. The footprint can't be seen but dust lifted off the paper to see the print on foil will show the unique footwear marks that are made by an individual because of the way he or she 'treads' and wears the shoes. Forensic chemistry also looks at paint comparisons - a trace of paint in a hit and run accident can link back to a vehicle. Marie illustrated the point in a local case where a kidnapper hit a tree before making his escape. Laboratory analysis of the paint left on the tree was able to confirm manufacture of the car and the year it was made allowing the police to quickly identify local suspects and find the kidnapper. Chemical etching is another technique employed to uncovered erased serial marks. The plate can be dipped sulphuric acid to find out the original marks. Firearms Discharge Residue analysis is another area of investigation. Residue can be found on hands, clothing and in vehicles - part of the evidence used to 2
convict the killer of Gill Dando was one particle of firearm residue. Forensic chemists can classify the make of the firearm and link the bullet to the gun. UV traps are used to mark money in, for example, a company office, which is experiencing an outbreak of theft. Chemicals on the marked money is made with a special, secret combination known only to the police. A swab from the suspect's hand will confirm the combination. The combination of chemicals eliminates contamination from possible sources other than the marked money - such as, strangely enough, oranges. Forged signatures, photocopies, handwriting, document alterations are also studied using ESDA examinations for different indentations of writing. A vast amount of laboratory testing is done at the Strathclyde forensic biology department to answer questions about body fluids, whether they are human, where they come from and whose is it. A KM test that reacts with haemoglobin in blood confirms that a substance is indeed blood. Blood pattern analysis will answer further questions and give clues to building a picture of what has actually happened in an incident. A suspect has blood on his or her clothes but how the blood is on the clothes offers clues to the participation in the incident. Blood stains indicate direct blood touching which could mean the suspect has cradled the victim or tried to help. Blood spots on clothes tell a different story as spots can only be caused by violent impact, which would disprove a suspect's claim that he was trying to help the victim. Marie Campbell showed examples of this with photos of a pair of trousers showing the blood spot splatter caused by kicking the victim and a jacket with contact bloodstains of a passer-by who has stopped to help the victim. Analysis also looks at the lines of blood flying from the weapon as it is brought up and then down on a victim. Blood analysis determines species identification and blood grouping using two systems - DNA profiling or PCR. The laboratory will analyse 10 areas of DNA and conduct sex test that ensure the chances of a false identification are one in a billion. The advantages of DNA testing are that very small sources can be used and information can be extracted from very old stains. Testing can also be done on different sources such as hair although it has to have root material for successful testing. DNA testing can also be done on semen, body tissue such as deep muscle tissue within a decomposed torso, saliva (cigarette ends, bottles, gags, stamps) and skin cells found in faeces, urine, sweat and dandruff. Urine itself does not contain DNA - it is the cells being passed through urine that carries 3
Page 1: Investigating CSI - Background mate
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Page 11 and 12: Matching DNA Proving that a suspect
Page 13 and 14: Creating a DNA Profile: The Basics
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Page 21 and 22: II. Tools and Techniques for DNA Fo
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The Federal Bureau of Investigation
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III. Interesting Cases Using DNA Ev
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