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Legal Standards and Procedures
Whether scientific is admissible in criminal cases depends on:
- The evidence tends to prove or disprove a fact that, under the applicable law
- The expert presenting the evidence is qualified
- The information is derived from scientifically acceptable procedures
- Whether the potential for unfair opinion or time consumption substantially
out weighs the probative value of the information
The General-Acceptance Standard
- The Frye Standard
oThe proponent of the scientific evidence must establish that the
underlying theory and methodology are generally accepted .
oIs it admissible in court
oCame from the admissibility of a polygraph test
- Instead of the Frye test
- The court prescribed a broader framework for deciding whether proposed
testimony has sufficient scientific validity and reliability
- Was based on a medication that was said to be safe for pregnant women.
First- scientific knowledge
Second- it must assist the trier of fact in understanding the evidence or determining
a fact in issue in the case.
Third- that the judge would make the threshold determination- regarding whether
certain evidence should be heard.
Reasoning or Methodology
- Has the tech been tested in actual field conditions?
- Has the technique been subject to peer review & publication?
- What is the known or potential rate of error?
- Do standards exist for the control of the technique’s operation?
- Has the technique been generally accepted within the relevant scientific
Should be examined by the court to see if evidence should be admissible
Preliminary assessment of whether the reasoning or methodology underlying the
testimony is scientifically valid.
Expert Witness Testimony
- Both pros and defense
- Findings or opinions of forensic expert wit., may either be presented as
reports, or appear in court.
- Specialized in a specific area
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Function- commonly used in court by both the pros and defense to establish
credibility of a person on the stand
Significance- opinion of forensic examiner is a spec. field to be used in court as
Types- can come from almost any professional field. Medicine, law,
Hair and Fibre Analysis
- Hair and fur
- Info obtained by hair analysis
- Methods of analysis
- Microscopic structure of hair
- Fibers as trace evidence
- Other methods of analysis
- Hairs and fibers as an evidence
- Hair analysis in the court
Hair and Fur
Def: natural fibers of animal origin. Hairs are animal fibers that originate from
humans, while furs originate from other species.
No special qualifications necessary. Just take a course
Information obtained by hair analysis
- Is the examined item actually hair?
- Is it a human hair or fur (what kind)?
- Is it male or female hair?
- Is it infant or mature adult hair?
- Race: Caucasian, black or Asian?
- Hair forcibly removed, cut or fallen?
- From which part of the body? (pubic, scalp…)
- Traces of drugs or chemicals
- Identifiable illness or special conditions
- DNA analysis: STRs somatic & Y chr., mitochondrial
Methods of Analysis
- Largely centered on microscopy. The principle goal is to establish a common
origin between known and recoverd samples in a criminal case.
-What to compare in hair analysis?
oMicroscopic characteristics: up to 24 charact. (cortex, cuticle,
root, cortical fusi, ovoid bodies, pigment and pigment dispersal, cuticle
thickness, gaping, and whether the hair had been dyed or specially
treated) Will show a probability if many of these characteristics are
the same or strongly similar- finding common origin.
-Microscopic structure of Hair:
oA typical hair can be thought of as resembling a lead pencil.
Examine the Tip to End. Comparisons
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