Physical EvidencePhysical Evidence

Any material either in gross or tracequantities that can establish throughscientific examination and analysisthat a crime has been committed.

Forensic laboratories

identification

Items of physical evidence

evaluation individualization

E x a m in a t io n a n d a n a ly s is o f p h y s ic a le v id e n c e

p h y s ic a lid e n t i f ic a t io n

H ig h e s t d e g r e e o f s c ie n t i f ic c e r ta in t y p o s s ib le w i thc u r r e n t t e c h n o lo g y

c h e m ic a lid e n t i f ic a t io n

b io lo g ic a lid e n t i f ic a t io n

Physical EvidencePhysical Evidence

Any material either in gross or tracequantities that can establish throughscientific examination and analysisthat a crime has been committed.

Classification of Physical EvidenceClassification of Physical Evidence

• Trace evidence

• Direct evidence

• Prima facie evidence

• Circumstantial evidence

• Exculpatory evidence

extremely small items

stands on its own to prove an alleged fact

evidence established by law

incriminates a person

helps to prove that an accused individual is not guilty

Forensic laboratories

identification

Items of physical evidence

evaluation individualization

Topic I: Probability

• Class characteristics

• Individual characteristics

features that place the

item into a specific

category

features that distinguish one item from another of the same type

Topic I: Probability

Evidence Analyte/Characteristic TechniquesBlood Ethanol

Drugs of abuse Headspace analysis GC GC/MSFabric Composition FT-Raman spectroscopy

Color Visible, diffuse reflectance spectroscopyFibers Composition FT-IR microscopy

Physical properties Solubility, melting point Shoes Miscellaneous Solid-phase extraction; LCPowder Drugs of abuse FT-IRSoil pH Potentiometry

Iron UV-Visible Spectr. Saliva stain Proteins Immunological tests

DNA Short tandem repeat DNA analysisClothing Visible reflectance, FT-IR microscopy, FT-

RamanPen inks UV–vis, Liquid CromatographyPlastic fragments FT-IR, UV–visTire fragments Thermal analysis, FT-IRFood (poisoned) Liquid- and solid-phase extraction, GC/MSFingerprints Fluorescent visualizationArson samples GC, GC/MS

Topic II: Analytical Techniques

One morning in the summer of 1961, hundreds of crazed birds attacked the seaside town of Capitola, California. The birds "cried like babies" as they dove into streetlamps, crashed through glass windows, and attacked people on the ground. Most of the birds were sooty shearwaters, a normally nonaggressive species that feeds on small fish and comes ashore only to breed. The incident fascinated Alfred Hitchcock, who frequently vacationed in nearby Santa Cruz. He included newspaper clippings about the Capitola attack in his studio proposal for The Birds, which appeared in cinemas two years later.

In the winter of 1987, the agent that is now believed to be responsible for the Capitola incident struck on the opposite shore of the continent. This time, it struck higher on the food chain. Over a hundred people became extremely ill within hours after dining on cultured blue mussels in restaurants around Prince Edward Island in Canada. It quickly became apparent that this was no ordinary outbreak of food poisoning. Vomiting, cramps, diarrhea, and incapacitating headaches were followed by confusion, loss of memory, disorientation, and (in severe cases) seizures and coma. A few exhibited emotional volatility, with uncontrolled crying or aggressiveness. Three elderly victims died. [Perl].

A tragic symptom of poisoning was the destruction of short term memory in about one quarter of the survivors. They could remember nothing that happened after the poisoning. Some were unable to recognize their surroundings or relatives. They could learn no new facts or skills. The most severely affected lost memories several years old. For twelve of the victims, the loss of short term memory was permanent.

Case Study

Figure 1. General strategy for isolation of the toxin responsible for amnesic shellfish poisoning. Based on a diagram by M. Quilliam and J. L. C. Wright (Analytical Chemistry, 61, 1054 (1989)).

Domoic acid in acidic solution. Glutamic acid in acidic solution.

A band very close to the band for glutamic acid was observed in the electrophoresis of the toxic XAD-2 fraction, but not in the control fraction. It stained a distinctly different color from the glutamic acid. When the material in the band was collected and injected onto the HPLC column, it took exactly the same amount of time to move through the column as the toxic component found by the HPLC analysis. It also produced exactly the same amount of toxicity as the HPLC fraction had. Mass spectrometry was used to determine the compound's molecular weight (312 g/mol) and molecular formula (C15H22NO6). Spectroscopic analysis revealed the presence of conjugated double bonds and features characteristic of an amino acid. By matching the spectra with those from STN International's Registry system, the compound was unambiguously identified as domoic acid, an triprotic amino acid:

Domoic acid is a molecular Trojan Horse. Nerve cells mistakenly recognize domoic acid as glutamic acid- a fatal error. Domoic acid's structure is obviously similar to glutamic acid. But its five-sided ring makes it less flexible than glutamate, which causes it to bind very tightly to glutamate receptors. As a result, the excitatory effect of domoate is 30 to 100 times more powerful than that of glutamate [Perl].

The standard deviation (SD) quantifies variability. If the data follow a bell-shaped Gaussian distribution, then 68% of the values lie within one SD of the mean (on either side) and 95% of the values lie within two SD of the mean. The SD is expressed in the same units as your data.

The arithmetic mean is the "standard" average, often simply called the "mean"

Topic III: Statistics

Case Study

Table Bullets and fragments received by the FBI.

Specimen Description Total weight, grains Total weight,mg

CE 399 (Q1) Bullet from stretcher (lead core plus jacket) 158.6 10,277

CE 567 (Q2) Bullet fragment from seat cushion (lead core plus brass jacket) 44.6 2,890

CE 569 (Q3) Bullet fragment from front seat (jacket) 21.0 1,361

CE 843 (Q4,5) Two lead fragments from President’s head[2] 1.65; 0.15 107; 9.7

CE 842 (Q9) Three lead fragments from Connally’s arm 0.5 32

CE 840 (Q14) Three lead fragments from rear carpet 0.9, 0.7, 0.7 58, 45, 45

CE 841 (Q15) Scraping from inside surface of windshield None listed

Specimen Weight of subfragment, mg Sb, ppm

Q1 7.16 643

4.20 636

1.79 750

1.24 749

1.16* 749

15.55 705±60*

Table : Individual determinations of antimony in the FBI’s Run 4

Specimen Weight of subfragment, mg Sb, ppm

Q9 1.92 690

2.07 662

1.34 677

5.33 676±14

Table : Individual determinations of antimony in the FBI’s Run 4

• BODY FLUIDS Conventional serology:

presence of blood in stainsspecies identification and

ABO groupingis not adequately

informative to positive identify a person

DNA analysis can associate victim and/or suspect with each other or with the crime scene

• BLOODSTAIN PATTERNS additional information

SEM: erythrocytes & lymphocytes

Topic IV: DNA fingerprinting

• FIRE DEBRIS & EXPLOSIVES RESIDUE EXAMINATIONS

identification of accelerants and explosive residues Unburned accelerator liquid on a soot covered carpet

Topic V: Arson and Explosives

• BODY TISSUES organ samples collected at

autopsy, including blood, urine and stomach contents

• DRUGS & CONTROLLED SUBSTANCES plant materials, powders,

tablets, capsules

toxicological analysis volatile compounds (ethanol,

methanol, isopropanol) heavy metals (arsenic) nonvolatile organic compounds

(drugs of abuse, pharmaceuticals) miscellaneous (strychnine,

cyanide)

trace drug presence, identity,

and quantity

Black tar heroine wrapped in cellophane

Topic VI: Toxicology