Forensic Chemistry Notes from Transcript

CSI Basics and Core Definitions

1. CSI (Crime Scene Investigation/Investigator)

2. Corpus delicti: the body of crime; proof that a crime occurred is required for conviction.

3. Druggist’s fold (evidence fold): method for wrapping small evidence to prevent loss, then placed in standard packaging to prevent leakage.

4. Exemplars: baseline, known evidence (fingerprints, DNA, hair, voiceprints) collected from suspects or victims for comparison.

5. Modus Operandi (MO): Latin for "mode of operation"; criminal’s pattern or method used to commit a crime.

6. PMI (Postmortem Interval): time from discovery of a dead body to the time the victim died.

7. Probative evidence: evidence that tends to prove or disprove a fact in issue.

8. Protocol in investigations: detailed, established plan or procedure that must be followed for evidence to be valid in court.

9. Four basic search methods at crime scenes:

   • Spiral

   • Grid

   • Line

   • Zone search patterns

10. Documentation in crime scene work: recording in detail the conditions and labeling the location of each piece of evidence.

11. Preliminary Scene Examination: initial CSI unit examination to identify safety hazards, establish scene boundaries, and begin planning.

Scene Processing and Documentation

1. Four basic steps in systematic search and documentation:

   • Preliminary examination

   • Systematic search

   • Photographing/recording

   • Documentation of findings (with evidence collection)

2. Purpose of recording the crime scene with photography and sketches:

   • Document the scene for accurate reconstruction and later court presentation.

   • Digital photos and walk-through videos are common.

3. Total Station: digital mapping device using a laser range finder to measure coordinates and angles, enabling 3D documentation.

4. GPS in crime scene documentation: used to document locations and coordinates, especially in remote or outdoor scenes.

5. Chain of custody: physical log documenting who had possession of evidence and when, from collection to court.

6. Tamper-evident packaging: sealable container/tape that shows if it has been opened; preserves evidence integrity (note: "tamper-proof" does not exist).

7. Key elements of the chain of custody:

   • Documentation of possession

   • Unique identification (e.g., barcode)

   • Tamper-evident packaging

   • Signed custody transfer records

8. One-item-per-container: important to prevent cross-contamination and preserve integrity.

9. Three major steps in evidence collection:

   • Recognition of evidence

   • Collection of evidence

   • Packaging/preservation (followed by delivery to the lab)

10. Physical vs nonphysical evidence:

    • Physical: tangible objects.

    • Nonphysical: testimony, observations, behaviors.

11. Real evidence vs demonstrative evidence:

    • Real: produced by the crime (e.g., fingerprints, bullets).

    • Demonstrative: illustrates or explains real evidence (e.g., sketches, models).

12. Known vs unknown evidence:

    • Known: has a known source.

    • Unknown: source not known at discovery; must be determined.

13. Begin planning the investigation: initiate planning activities as part of scene processing.

Evidence Types, Controls, and Testing

1. Individual evidence vs class evidence:

   • Individual: tied to a single source.

   • Class: narrows to a group, not a unique source.

2. Positive and negative controls:

   • Positive: shows what a true positive looks like.

   • Negative: shows a true negative, guarding against false results.

3. False positive test: incorrectly yields a positive result when the substance is not present.

4. False negative test: incorrectly yields a negative result when the substance is present.

5. Fingerprint analysis detail levels:

   • Level 1: overall pattern.

   • Level 2: minutiae details.

   • Level 3: very fine details (pores, sweat glands).

6. DNA evidence vs other pattern evidence:

   • DNA typing compares multiple loci, yielding a probabilistic match.

   • Chance of a random match is astronomically low, providing strong individualization.

7. NAS concern about pattern evidence: lack of standardized validation, data on error rates, and clear definitions of matches.

8. OSAC (Organization of Scientific Area Committees for Forensic Science): develops robust standards and recommended practices.

9. FEPAC (Forensic Science Education Program Accreditation Commission): accredits BS and MS forensic science degree programs.

10. Federal forensic laboratories and their agencies:

    • FBI Laboratory (DOJ)

    • DEA laboratories (Drug Enforcement Administration)

    • BATF laboratories (Bureau of Alcohol, Tobacco, Firearms and Explosives)

    • Others: Secret Service, IRS labs

11. Difference between crime scene investigation and forensic science:

    • CSIs: collect and document evidence at the scene.

    • Forensic scientists: analyze evidence in the lab and provide expert testimony.

12. Purpose of accreditation: ensure laboratories follow standardized procedures, produce reliable results, and examiners are certified.

Laboratory Methods, Standards, and Forensics Infrastructure

1. Chromatography in general: family of separation techniques based on attraction of analyte components to stationary vs mobile phases.

2. Three common chromatography types in forensics:

   • Gas chromatography (GC)

   • High-performance liquid chromatography (HPLC)

   • Thin-layer chromatography (TLC)

3. GC-MS (gas chromatography–mass spectrometry): separates compounds (GC) and identifies them by their mass spectra (MS), providing definitive identification.

4. Pyrolysis GC: GC analysis of high-boiling polymers by heating to decompose them into characteristic fragments.

5. Electrophoresis and its use: separation technique using an electric current; gel and capillary electrophoresis separate DNA fragments.

6. TLC (thin-layer chromatography) in forensics: versatile, low-cost method for presumptive analysis of drugs, inks, explosives; detects via color or fluorescence.

7. Like dissolves like rule: polar solutes dissolve best in polar solvents, nonpolar in nonpolar; solubility depends on matching polarity.

8. pH: negative logarithm of hydrogen ion concentration; acids ( < 7), bases ( > 7), pure water ($= 7$). Expressed as $ext{pH} = -ext{log}_{10} [ ext{H}^+].$

9. Liquid–liquid extraction: separation using two immiscible solvents to extract a solute based on polarity and acidity/basicity differences.

10. Solid-phase extraction: adsorbing the analyte onto a solid adsorbent and then desorbing for analysis.

11. Case of Helle Crafts: example illustrating reconstruction of a murder without a body (highlights evidentiary reconstruction from non-biological trace/indirect evidence).

12. Purpose of calibration and accreditation in forensic science:

    • Calibration: ensures instruments provide accurate measurements.

    • Accreditation: ensures labs follow standardized procedures and maintain quality control, contributing to reliable results.

13. Example case (calibration/accreditation in practice): illustrative case showing how CSI and evidence collection can reconstruct a murder without a body.

Evidence Provenance, CSI Effect, and Ethical Considerations

1. Proof that a crime occurred: establishing death or other crime evidence to convict (e.g., murder) based on collected evidence.

2. National Commission on Forensic Science (NCFS): provided guidance and recommendations on standards, accreditation, and ethical use; superseded by NCFS activities moving to DOJ/NIST via OSAC.

3. CSI effect: jurors may expect investigators to collect every possible piece of evidence, pressuring investigators to over-collect.

4. Real evidence vs demonstrative evidence (revisited): real evidence derives from the crime; demonstrative evidence illustrates or explains real evidence.

5. Provenance of evidence: the source or origin of evidence; unknown evidence must be connected to a known source.

6. Corpus delicti (forensic context): concept in proving that a crime occurred, used to authorize conviction after establishing the crime and the accused's involvement.

Miscellaneous and Recap

1. Key distinctions to remember:

   • Real evidence vs demonstrative evidence

   • Individual vs class evidence

   • Known vs unknown evidence

   • Positive vs negative controls

2. Common workflow recap:

   • Recognition and identification of evidence

   • Collection and packaging/preservation

   • Documentation and labeling

   • Transport to lab

   • Analysis with validated methods

   • Comparison to known exemplars

   • Court presentation with proper chain of custody and provenance

3. Core aims of forensics infrastructure: standardized procedures, reliable results, and admissible expert testimony through accreditation, standards, and oversight bodies (OSAC, NAS concerns, NCFS/DOJ/NIST lineage).

Quick Reference: Key Terms

• Corpus delicti: the body of crime; proves that a crime occurred.

• Modus operandi (MO): a criminal’s pattern or method.

• PMI: postmortem interval (time since death).

• Chain of custody: documentation of possession of evidence from collection to court.

• Tamper-evident packaging: seals/evidence containers that show access.

• Real evidence vs demonstrative evidence: source vs illustrative.

• Positive/negative controls: test validity indicators.

• OSAC: standards and recommended practices in forensic science.

• FEPAC: accreditation for forensic science degree programs.

• GC, HPLC, TLC: chromatography techniques; GC-MS combines separation and identification.

• pH: acidity/basicity scale; formula shown above.

• Liquid–liquid extraction; solid-phase extraction: separation techniques based on polarity and adsorption.

• Helle Crafts case: example used to demonstrate reconstruction without a recovered body.

• CSI effect: juror expectations influencing investigative over-collection and procedures.