Reference for slides 3 – 20: Forensic Science (科學鑑證) Criminalistics – An Introduction to Forensic Sciences, 7th ed. By Richard Saferstein Prentice­Hall, NJ, c2001. IJSO Training (Phase 3) Dr. Kendrew K. W. Mak Department of Chemistry The Chinese University of Hong Kong 2 1 Definition and Scope of Forensic Science The Basic Services Provided by Crime Laboratories Forensic science (科學鑑證): The application of science to law. Basic Services Provided by Full­Service Crime Laboratories 1. Physical Science Unit Apply the principles and techniques of sciences to the analysis of evidence recovered during crime investigation. 2. Biology Unit 3. Firearms Unit Provide expert court testimony (證據). 4. Document Examination Unit 5. Photography Unit The procedures and techniques used must: • have a firm scientific foundation • be admissible (可採納的) to the courts. 3 The Basic Services Provided by Crime Laboratories 4 The Basic Services Provided by Crime Laboratories Physical Science Unit: Use scientific tests and modern analytical instruments to identify and compare crime­scene evidence. E.g. drugs, glass, paints, explosives and soil…… Document Examination Unit: Study handwriting and typewriting on questioned documents to establish authenticity and/or source. Analysis of paper and ink, erasures, and burned or charred documents. Biology Unit: Identifying and DNA profiling of dried bloodstain (血跡) and other body fluids. Comparison of hair and fibers. Identification and comparison of plants. Photography Unit: Examine and record physical evidence using special photographic techniques to make invisible information becomes visible. E.g. digital imaging, infrared (紅外線), ultraviolet (紫外線), and X­ray photography
Firearm Unit: Examine firearms, discharged bullets, cartridge cases (子彈殼), shotgun shells, and ammunition (彈藥) of all types. Detect firearm discharge residues on garments and other objects. Estimate the distance from which a weapon was fired. 5 6 Optional Services Provided by Crime Laboratories Processing the Crime Scene Physical Evidence: Establishing that a crime has been committed Providing a link between a crime and its victim or a crime and its perpetrator. Optional Services Provided by Crime Laboratories 1. Toxicology (毒理學) Unit 2. Latent Fingerprint (潛伏指紋) Unit 3. Polygraph (測謊) Unit 4. Voiceprint Analysis (聲紋分析) Unit 5. Evidence­Collection Unit Collected by experts who are very knowledgeable in crime laboratory’s techniques, capabilities, and limitations. Forensic science begins at the crime scene. If a physical evidence was not properly collected and preserved, it is useless. 7 8 Processing the Crime Scene (犯罪現場) Processing the Crime Scene The Key Steps: Secure and isolate the crime scene: Exclude all unauthorized personnel from the scene ­ to prevent destruction of the important physical evidence. 1. Secure and isolate the crime scene 2. Record the scene – by photography, sketches and notes 3. Conduct a systematic search for evidence Record the scene: Permanently record the scene in its original state – to document the condition of the crime site and to record the location of physical evidence. 4. Collect and package physical evidence 5. Maintain chain of custody (保管鏈 / 保管流程) 6. Obtain controls 7. Submit evidence to the laboratory photography, sketches, and notes 8. Crime­scene safety Conduct a systematic search for evidence: The search for physical evidence at a crime scene must be thorough and systematic – to collect as much relevant evidence as possible. 9 10 Processing the Crime Scene Processing the Crime Scene Collect and Package Physical Evidence Prevents any change from taking place between the time it is removed from the crime scene and the time it is received by the crime laboratory. Obtain Controls The examination of evidence often requires comparison with a known standard or control (對照). Such materials may be obtained from the victim, a suspect, or other sources. Avoid contamination (污染), breakage, evaporation, accidental scratching or bending, or loss through improper or careless packaging. Crime­scene Safety All items must be packed separately to prevents damages and cross­ contamination. Maintain Chain of Custody Continuity of possession, or the chain of custody, must be established. 11 • Forensic and crime­scene personnel may encounter potentially infectious materials that collected from the scenes (e.g. blood) • Alert to sharp objects, knives, hypodermic syringes (皮下注射針
筒), razor blades (剃刀刀片), etc. • Avoid contamination of pens, pencils, notebook, paper, etc.
12 The Significance of Physical Evidence The Significance of Physical Evidence Common Types of Physical Evidence Examination of physical evidence for identification or comparison. Identification To determine the physical or chemical identity of a substance using modern analytical techniques (分析技術). Comparison Perform the same tests and examinations to the suspect and control specimens to determine whether they have a common origin. 1. Blood, Semen (精液), and Saliva (唾液) 11. Organs (器官) and Physiological Fluids 2. Documents 12. Paint 3. Drugs 13. Petroleum Products (石油產品) 4. Explosives 14. Plastic Bags 5. Fibers 15. Plastic, Rubber and Other Polymers 6. Fingerprints (指紋) 16. Powder Residues (殘餘物) 7. Firearms and Ammunition 17. Serial Numbers 8. Glass 18. Soil and Minerals (礦物質) 9. Hair 19. Tool Marks 10. Impressions 20. Wood and Other Vegetative Matter 13 Fundamental Principles of Fingerprints 14 Methods of Detecting Fingerprints Three Types of Fingerprints: 1 st Principle: A fingerprint is an individual characteristics. Visible prints: Made by fingers touching a surface after the ridges have been in contact with a colored material such as blood, paints, grease (油脂), or ink. Theoretical calculation – 64 billion different fingerprints. No two have even been found to be identical. Plastic prints: 2nd Principle: A fingerprint will remain unchanged during an individual’s lifetime. Ridge impressions left on a soft material such as putty (油灰), wax, soap, or dust. Latent prints: 3 rd Principle: Fingerprints have general ridge (脊) patterns that permit them to be systematically classified. Or invisible prints. Impressions caused by the transfer of body perspiration (汗水) or oils present on finger ridges to the surface of an object. 15 Methods of Detecting Fingerprints 16 Methods of Detecting Fingerprints Super Glue Fuming Super glue consists of almost pure ethyl­2­cyanoacrylate. The method used for visualizing a latent print depends on the type of surface that is being examined. The invisible fingerprints residues react with the CA (cyanoacrylate ­ 氰基丙烯酸
酯) fumes and atmospheric moisture to form a white polymer (polycyanoacrylate) on the fingerprint ridges and become visible to the naked eyes. Hard and nonabsorbent surfaces (e.g. glass, mirror, tile, and painted wood) Developed by the application of a powder (adhere to perspiration residues and/or body oils left on the surface) or treatment with Super Glue ® Soft and porous (多孔) surfaces (e.g., papers, cardboard, and cloth) Treatment with one or more chemicals e.g. Iodine (碘), ninhydrin (寧希德林), and silver nitrate (硝酸銀). 17 Spray with Ninhydrin Solution Ninhydrin reacts with the residual amino acids (氨基酸) present in trace amounts of perspiration and forming visible purple­blue colored prints. CN O OCH 2 CH 3 ethyl­2­cyanoacrylate O O H O H O ninhydrin
18 Different Types of Chromatography (色層分析法) Thin­layer chromatography (薄層色層分析法) Column chromatography (柱色層分析法) Thin­Layer Chromatography A very important technique for rapid and qualitative analysis (定性
分析) of small amounts of material. Suitable for the analysis of mixtures in small and microscale experiments, without the need for expensive instrument. solvent front TLC sheet containing a thin layer of adsorbent (吸附劑) solvent move up by capillary action (毛細管作用) separated components time Original sample spot immense in eluting solvent The original spot should not be immersed in the eluent (洗提液). Recall your experience with paper chromatography. (紙色層分析法) 19 20 Thin­Layer Chromatography (TLC) The Adsorption Process Chromatographic Method • Chromatography ­ the separation technique based on the selective distribution of chemicals between a stationary phase (固定相) and a mobile phase (流動相) • Due to the selective interaction of chemicals with the stationary and mobile phases, separation is achieved after a certain period of time. Types of Chromatography • Thin­Layer Chromatography (TLC) Column Chromatography • • Instrumental Technique Gas Chromatography (氣相色層分析法 ) (GC or GLC) High­Performance Liquid Chromatography (高效能液相色譜法) (HPLC) • • Strictly a surface process Depends on electrostatic forces (靜電力) (dipole­ dipole, ion­dipole and H­ bonds) Common adsorbents for TLC (a more effective version of paper chromatography) • Adsorption (吸附作用) 21 Thin­Layer Chromatography (TLC) The Adsorption Process • Silica gel (硅膠) (SiO 2 ): has polarized (極化) Si­O and O­H bonds that interact with dipole (偶極) in the solutes (溶質) • Alumina (氧化鋁) (Al 2 O 3 ) (The activity of the stationary phase partially depends on its water content) 22 Equipment For Thin­Layer Chromatography TLC Plate Silica gel coated on an aluminium backing sheet TLC Developing Chamber
23 24 Procedure For Thin­Layer Chromatographic Analysis • Visualizing The Developed Plate (Fluorescent Indicator熒光指示劑) Carefully apply a small drop of the sample solution to a chromatographic plate near the edge of a narrow end. If the compounds in the sample are colorless, they must be made visible by some visualizing reagents or methods. (Handle the strip only by the sides to avoid Visualization with fluorescent indicator contaminating the plate with oils from your fingers.) • Prepare the developing chamber. • Place the TLC plate with spotted end down in a closed jar. Many commercially available pre­made TLC plates are coated with fluorescent indicator (熒光指示劑). When a developed TLC plate is held under ultraviolet (UV) irradiation, spots that either quench or enhance fluorescence can be seen. (The level of the eluent should be just below the sample spot) • When the solvent front has advanced nearly to the top of the TLC plate, the development of the chromatogram (色譜展現) is complete, and the plate is withdrawn from the developing chamber. 25 Visualizing The Developed Plate (Fluorescent Indicator) TLC adsorbents come with zinc sulfide (硫化鋅) (will fluoresce green under 254 nm wavelength light) A dark spot appear where there is an eluted substance which quenches this fluorescence. Applications Compounds that absorb UV at 254 nm • Aromatic compounds (芳香族化合物) • Conjugated alkenes (共軛烯烴) • Conjugated carbonyl compounds (共軛羰基化合物) (ketones 酮 , aldehydes 醛 , esters 酯 ……)
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