Download Forensic Science

Forensic Science
Prof. Dominic T.W. Chan
Department of Chemistry, CUHK
Rm. SC 163 (South Wing)
Tel: 2609-6260
Email: [email protected]
Definition of “Forensic Science”
•
The term “forensic” comes from the Latin word forum,
which means “the market-place”. In Roman society, justice
was administered in the market-place.
•
Forensic Science is the study of objects (or evidence) that
relate to a crime.
•
Forensic Scientists observe, classify, compare, use numbers,
measure, predict, interpret data, and draw inferences, or
reasonable conclusions based on evidence.
Objectives
•
This presentation will introduce some of the experimental
methods used by forensic scientists for inspecting common
evidence, such as fingerprint, suspected drugs, explosives
and bloodstains.
Organization Chart of Government Laboratory
Government Chemist
Analytical & Advisory
Services Division
Forensic Science
Division
Physical & Biochemical
Evidence Group
•
•
•
•
•
Biochemical Sciences
Chemical Sciences
Physical Sciences
Questioned Documents
Scene of Crime
Administration
Division
Drugs & Toxicology
Group
• Controlled Drugs
• Forensic Toxicology
Fingerprints
•
A freshly formed fingerprint contains approximately 1 µg of
materials and consists mainly of sweat (99% water, sodium
and potassium chloride). There are trace amounts of amino
acids and urea plus fatty substances transferred from other
parts of the body to the fingers.
H2N
Amino acid
C
COOH
H R
O
Urea
H3N
C
NH3
Fatty substances
e.g. Undecan-2,6-dienoic acid
COOH
Common Fingerprint Patterns
Plain Arch
Tented Arch
Loop
Central Pocket Loop
Plain Whorl
Double Loop
Developing Latent Fingerprints
A. Dusting for fingerprint
• for firm smooth surfaces, e.g. drinking glass or window
• two common powders
(i) vegetable black, a fine
carbon powder, for lightcolored surfaces
(ii) aluminum powder, a fine
white powder, for darkcolored surfaces
Developing Latent Fingerprints
B. Cyanoacrylate (Superglue) Fuming method
•
•
Superglue vapor polymerizes on latent fingerprints to
produce a white deposit.
For flexible and rough surface, e.g. aluminum foil, paper,
wood and plastics.
A-
CN
H2C
C
COOR
H2C
+
C
-
CN
A-
CN
COOR
C
-
A
COOR
CN
H2C
POLYMER
C
COOR
CN
Further
Reaction
A
C
COOR
CN
C
-
COOR
•
Ninhydrin spray is also used on crime scenes to visualize
fingerprints, which contain trace amount of amino acids.
O
O
OH
OH
NH2
+
H
R
OH
H
COOH
O
Ninhydrin
Amino acid
RCHO
+
+
CO2
+
O
NH3
Hydrindantin
(partially reduced ninhydrin)
O
O
OH
OH
N
O
+ NH3
O
OH
H
O
Condensation
reaction
O
OH
O
Ruhemann’s purple
(a blue-purple pigment)
Advanced techniques for developing fingerprints
C. Laser luminscence
Principle of Laser-induced fluorescence
Blood spatter analysis
90°
70°
50°
30°
20°
10°
Medium velocity impact
blood spatter on vertical surface
Medium-velocity impact
blood spatter on horizontal
surface
Genetic Fingerprinting - DNA fingerprinting
Blood sample
from suspect
Gel electrosphoretic
Analysis
DNA extract
Dried
bloodstain
Radioactive labelling
of the hypervariable
element& photographic
imaging of the labelled
sequences
DNA digested with
restriction endonuclease
A DNA fingerprint testing for paternity
Father
Mother
Child 3 - the one in question
Child 2
Child 1
From father
From mother
From neither the father
nor the mother
Mystery Powder and substances
• Abused drugs
• Suspicious fire
• Drunken driving
• Explosive & gunshot residues
Dangerous Drugs Ordinance in Hong Kong
“… over 930 drugs are subject to more regulatory
control than other over-the-counter drugs”
“… over 140 drugs ... are deemed to need more stringent
control owing to their propensity to being abused, which
may not only induce dependence in the abusers but
could be very detrimental to their health”
“… drugs with similar chemical structures are categorised
and controlled as a group, e.g. the “Phenethylamines”
group to which “Ecstasy” belongs”
Common abused drugs in Hong Kong
• Heroin (> 60%)
• Opium
• Cannabis
•Ice (methamphetamine hydrochloride)
• Phenethylamine or Ecstasy group (Rave Party drugs)
- MDMA, MDA, MDEA, MBDB
• Benzodiazepines
- Midazolam maleate, estazolam and
diazepam
• Ketamine
• Alcohol (uncontrolled drug except for drivers)
Structures of some common drugs
R1
R1 = -OH
R1 = -OH
R1 = -OAc
R2 = -OH
R2 = -CH3
R2 = -OAc
O
R2
Morphine
Codeine
Heroin
N
O
H
CH2CH3
N
CH2CH3
N
N
CH3
CH3
O
O
CH3
O
HN
Lysergic acid diethylamide (LSD)
O
H
Cocaine
C6H5
Methamphetamine
• Central nervous system stimulants, appetite suppressants and
dependence-forming
R = NH2
R = NHCH3
R = NH3CH3Cl
R
Amphetamine
Methamphetamine (MA)
Ice
“Ecstasy” or “rave party” drugs
• Central nervous system stimulants and a hallucinogen
• have evidence of permanent damage to the brain on prolonged use
O
O
R
R = NH2
3,4-methylenedioxyamphetamine (MDA)
R = NHCH3
3,4-methylenedioxymethamphetamine (MDMA)
R = NHCH2CH3
3,4-methylenedioxyethamphetamine (MDEA)
Common Benzodiazepines
• Some are used as sedatives or hypnotics, others used as
anxiolytics, muscle relaxants or anti-convulsants.
• Dependence, drowsiness, dizziness, sedation, depression & loss of
memory
O
N
HN
N
N
F
F
O2N
Cl
Midazolam maleate
(Dormicum
or Blue gremlin)
NHCH3
Cl
Cl
Cl
Flunitrazepam
(Rohypnol or Cross)
O
N
N
N
N
Ketamine
N
Triazolam
(Halicon
or Blue gremlin)
• Cause hallucinogens, visual
distortion, a loss of sense of
time, sense & identity, out-ofbody feeling.
Characterization and identification of drugs
Screening Tests
• Solubility tests
• pH test
• Spot or color tests
More Sophisticated Tests
• Immunoassays
• Chromatographic analysis
Immunoassays
• large proteins, called antibodies, can recognize and lock on to
specific smaller molecules, called antigens, to form a complex
Attachment of known
antibody to support
Addition of sample with
unknown amount of drug
Addition of excess
radiolabelled drug (antigen)
Incubation to establish
equilibrium
Wash to remove unbound
radiolabelled drugs
Wash to remove unbound
drugs
Measure the radioactivity of the
bound drugs
Chromatography
Gas chromatography
Screening of urine drugs using gas chromatography
1. Amphetamine
2. Methamphetamine
3. Meperidine
4. Phencyclidine
5. Methadone
6. Proposyphene
7. Amitriptyline
8. Cocaine
9. Imipramine
10. Cyheptamide
11. Codeine
12. Diazepam
13. Flunitrazepam
Other applications of chromatography in
forensic science:
• Identify drunken drivers
• Suspicious fire
Explosives and gunshot residues
A photograph
of a bullet
speeding
towards its
target
Explosives and gunshot residues
• A bullet
Cartridge case
Lead-Antimony core
Flash holes
Percussion
Cap
Anvil
Propellant (explosive)
Guilding
metal jacket
Well known explosives
CH3
O2N
NO2
No2
Trinitrotoluene (TNT)
Pentacrythritol tetranitrate
NO2
CH2ONO2
N
No2
N
N
O2NOH2C
NO2
CH2ONO2
CH2ONO2
Cyclotrimethylenetrinitramine
HPLC analysis of various additives
in a propellent
H
N
H
N
1. Diphenylamine
O2N
H
N
2. Carbazole
3. 2-nitrodiphenylamine
4. Dinitrotoluene
No2
CH3
NO2
5. N-nitrosodiphenylamine
O
N
N
6. 2,4-dinitrodiphenylamine
O2N
H
N
NO2
X-ray fluorescence analysis of gunshot residues
Pb
Fe
Sb
Ba
Secondary electron
Imaging of a gunshot
residue
X-ray fluorescence analysis
X-ray
He gas
sample
Be window
Detector
Amplifier
Energy
Analyzer
Be windows
X-ray tube
X-ray fluorescence
fluorescence
in X-ray range
Physical Examination
• Checking up on Suspicious Signatures
& Documents
• Accident reconstruction
• Contact evidence examination
• Precious metals/Gems analysis in
deception and theft cases
Analysis of questioned handwriting and
signatures
Top-of-letter handwriting
analysis
Botton-of-letter handwriting
analysis
Space analysis
Slant analysis
THE END
Assignment
Write an essay on the portable alcohol detector for
use in the field detection of drunken drivers