FOR10002 Lecture Notes - Lecture 2: Trace Evidence, Precipitin, Putty
FORENSIC SCIENCE - FOR10002
WEEK 2
The Role of Forensic Science in a Criminal
Investigation!
RECOVERY OF EVIDENCE
•How should evidence be handled in order to avoid contamination and how should it be
stored? !
•“Chain of custody” is the important feature !
EXAMINATION OF EVIDENCE
•Based on the theory “Every Contact Leaves a Trace” and is the principle behind most of our
lectures!
PRESENTATION OF EVIDENCE IN COURT SHOULD BE:
•Comprehensive !
•Understandable !
•Only rarely involves direct testimony !
•Then qualification and unambiguous statements are required !
QUALITY ASSURANCE
•Refers to the procedures put in placed to guarantee quality control!
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Collection of Trace Evidence!
FOA - FIRST OFFICER IN ATTENDANCE
•Obtain medical assistance for anyone in need !
•Arrest any perpetrators !
•Exclude all unauthorised personnel !
•Isolate the area!
SOCO - SCENE OF CRIME OFFICER
•CAP – common approach path !
-Minimise damage due to random traffic !
•Preservation of scene !
•Recording of scene !
•Logging of actions taken !
•Systematic search and recovery of evidence !
•Package, label and store any evidence!
PROPER PROTECTION OF EVIDENCE
•Dependent on type of evidence !
•Avoid handling items that could be tested for fingerprints !
•Airtight containers cause the putrefaction of wet or fresh blood samples !
•Cross-contamination can easily occur if two different pieces of evidence come in contact with
each other!
SAMPLE SUFFICIENCY
•Once a sample is collected from the crime scene then this becomes the maximum amount of
sample that can be tested !
•Collection of insufficient sample is usually due to improper training of crime scene investigators !
•Unable to recognise the quantity needed for the various tests that may be required!
KNOWN SAMPLES OR EXEMPLARS
•Used for comparison testing or matching !
•Must be obtained under the same conditions as when the evidence was generated !
•Handwriting samples obtained using the same writing implement, paper, posture, etc !
•Weapons tested using the same type of ammunition found at crime scene!
NEGATIVE CONTROLS OR “BLANKS”
•Required to eliminate contributions from the evidence that can influence the analysis technique!
-Test a piece of a similar unstained carpet to find if the carpet contains components that
interfere with the analysis of a blood stained carpet!
Preservation of Evidence!
Legal requirement that evidence is preserved in the same condition as it appeared at the crime
scene !
•If not properly preserved then it becomes inadmissible !
-Value diminished if rendered unfit for forensic analysis !
-Insufficient sample to be independently tested by defence !
•Court must be assured that the evidence is authentic !
-If the evidence spoils then it may lose its identifying characteristics!
Chain of Custody!
Initially all aspects of a crime scene need to be fully recorded !
•Crime scene photography !
•Documentation of evidence !
-Notes and sketches!
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find more resources at oneclass.com
A “chain of custody” records the transfer of evidence from the crime scene and there are two
parts !
•Process !
•Documentation!
CHAIN OF CUSTODY PROCESS
1. Identification of the evidence
The first step in the authentication chain requires identification of the evidence !
•The collected evidence is placed in a container where identifiers are recorded directly on
the container !
-Name or initials of collector !
-Date and time of recovery !
-Case and item numbers!
2. Proper Packaging
Proper packaging is required !
•Appropriate for the type of evidence !
•Tamper evident containers not tamper-proof!
3. Laboratory Testing
Not all evidence requires laboratory analysis !
•Evidence is submitted with a request for laboratory testing !
•Request form will contain: !
-Description of evidence !
-Type of analysis !
-Time, date and location of collection !
-Police identifiers!
4. Assign unique Laboratory Based Identifiers
•Commonly bar-coded labels are used !
•Samples scanned before each analysis is performed!
CHAIN OF CUSTODY — DOCUMENT
•Each piece of evidence is accompanied by a document that records important information !
-Describes the evidence !
-Has corresponding identifiers as the evidence container !
•Also contains places to record possession of the evidence !
-Where the evidence has been and who had control !
-Signatures and dates where transfer of possession occurs !
•Document may contain multiple sheets so that a receipt for possession can be easily collected !
•Document could be part of the container !
-An evidence bag that has writable sections!
Examination of Trace Evidence!
Comparison is the key:!
•Evidential object versus relevant database !
•Crime scene evidence versus suspect scene evidence !
•Either of the above versus evidence created by the investigation team!
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The role of forensic science in a criminal. Recovery of evidence: how should evidence be handled in order to avoid contamination and how should it be stored, chain of custody is the important feature. Examination of evidence: based on the theory every contact leaves a trace and is the principle behind most of our lectures. Presentation of evidence in court should be: comprehensive, understandable, only rarely involves direct testimony, then quali cation and unambiguous statements are required. Quality assurance: refers to the procedures put in placed to guarantee quality control. Foa - first officer in attendance: obtain medical assistance for anyone in need, arrest any perpetrators, exclude all unauthorised personnel, isolate the area. Soco - scene of crime officer: cap common approach path. Minimise damage due to random tra c: preservation of scene, recording of scene, logging of actions taken, systematic search and recovery of evidence, package, label and store any evidence.
