physical evidence chapter 4. ©2008 the mcgraw-hill companies, inc. all rights reserved. the crime...

Physical Evidence

Chapter 4

©2008 The McGraw-Hill Companies, Inc. All rights reserved.

The Crime Laboratory• Crime laboratories provide scientific forensic

support to policing agencies at various governmental levels (county, state, and federal).


The Crime Laboratory• A crime lab is often actually a large group of

laboratories under one roof. • Each laboratory specializes in its own area or branch

of science, such as pathology, toxicology, ondontology, or ballistics.


DNA Profiling• Today crime laboratories are capable of matching

suspects with even minuscule amounts of biological evidence from a crime scene where DNA is extracted from.

• DNA profiling – A process where DNA is extracted from

biological evidence samples collected at a crime scene and compared with samples taken from the victim and suspects.

– The DNA samples are analyzed and compared to determine whether they have a common origin.


DNA Profiling• DNA (deoxyribonucleic acid) is a molecule present in

all life forms.– Forensic scientists can get information about

the identity of biological evidence by conducting sophisticated laboratory tests on the DNA.

• The process begins when DNA is extracted from comparison samples collected from victims and suspects.

• The DNA samples are analyzed and compared to determine whether they could have had a common origin.


DNA Profiling• A genetic DNA profile can be used to:

– strongly link a suspect to a crime scene, a victim, a weapon

– turn attention away from a suspect• Each molecule of DNA is composed of a

long spiral structure that has been likened to a twisted ladder (the double helix).– The two parallel “handrails” of the ladder are

held together by a series of rungs.– Each rung on this twisted ladder consists of a

base pair, two of four varieties of nucleic acid. • The sequence of these rungs or base pairs

constitutes the genetic coding of DNA.


DNA Profiling• Base pair

– Two of four varieties of nucleic acid found on each rung of the DNA ladder.

• DNA in humans can be found in every cell that contains a nucleus, with the exception of red blood cells.

• The nucleus of cells (except sperm and egg cells) contains the full complement of an individual’s DNA.

• Genome – The full complement of an individual’s DNA.


DNA Profiling• The genome is identical in every cell of an

individual’s body.• The genome is composed of approximately 3

billion base pairs, among which only about 3 million or so differ from one person to the next, and from which various traits in people are affected.


DNA Profiling• The base pairs that vary, however, represent a virtually

incalculable variety of possible combinations.• Alleles

– Individual differences in base pairs in a DNA sequence.

• DNA fingerprinting – In its simplest form, this involves taking a specimen:

• slicing it into fragments• radiating these fragments• exposing them to X-ray film• The resulting line patterns on the film are the DNA

fingerprints.


DNA Profiling• Methods of DNA Testing

– Restricted fragment length polymorphism (RFLP) analysis

• Early method of DNA typing.– Polymerase chain reaction (PCR) analysis

• Small amounts of DNA are replicated to generate sufficient quantities of the material to be analyzed.

– Mitochondrial DNA (mtDNA) analysis • Biological evidence may be obtained from cells

lacking a nucleus such as hair shafts, bones, and teeth.


DNA Profiling

• Short tandem repeat (STR) loci – A standard battery of 13 core loci.– Each contains a short sequence of DNA that differ among

individuals and can be used for identification.

• CODIS – A computer network combining a database of several

indexes of DNA profiles obtained from:• criminal offenders• crime scenes• unidentified persons


How DNA Profiling is Performed


DNA Profiling

• Convicted offender index – Contains DNA profiles of individuals convicted of

felony sex offenses and other violent crimes.

• Forensic index – Contains DNA profiles created from various crime

scene evidence.


Submitting Evidence to the Lab

• Evidence transmitted to the laboratory for examination should be accompanied by certain information if the laboratory is to make a useful and complete comparison.

• Should include:– Administrative data– Summary of the case– Examinations requested– Urgency of the request


Blood as Evidence

• Common form of evidence found at a violent crime scene

• May be wet or dry• Dried spills or drops of blood are referred to as

bloodstains and may be interpreted.


The Significance of the Shape of Blood Stains


Blood as EvidenceThere are three common applications of blood evidence:

Finding blood:• with the victim’s genetic markers on the suspect• on something in the suspect’s possession• on something associated with the suspect

Finding blood:• with the suspect’s genetic markers on the victim’s• on something in the victim’s possession• on something associated with the victim

Investigative information determined from blood spatter or blood location (the nature of the attack, velocity and direction of impact, and so forth).


Blood as Evidence

• Reagents are the chemicals used to detect or test for the presence of blood or other substances.

• Luminol


Value in Cases

• Assault and Murder– Blood may be found on both victim and suspect– Clothing, weapons involved, and fingernail

scrapings

• Burglary– Broken windows, doorframes, floor

• Hit-and-Run Accidents– Points of impact and the undercarriage of the

vehicle


Value in Cases

• Rape– The clothing and especially the undergarments of

both the victim and the suspect


What Bloodstains Can Reveal• The location and appearance of the following can

sometimes provide information about how a crime occurred:– blood drops– splashes– spatter

• The shape of blood spots may permit an estimate of:– the velocity– the impact angle– the distance fallen from the source of the spatter– or all three

• The diameter of a blood spot is useful only for the first 5 or 6 feet from the impact.


Blood-Typing• Blood-typing

– Method of classifying blood into four major groups:• A, B, AB, and O• Another factor, called Rh factor, also helps determine a

person’s blood type, which is positive or negative for the Rh factor.

• Tests can determine whether a particular blood sample could have come from a specific person.


Blood-Typing

• Blood type and Rh factor cannot positively link a suspect to a crime scene, but they can positively rule out a suspect.


Possible Examination Results

• Laboratory examination of blood evidence can answer three main questions: Is the substance blood? If not, what is it? Is the substance human blood? If not, from what

animal did it come? If it is human blood, to what blood group does it

belong?


Semen as Evidence

• Semen and sperm, although frequently used as synonyms, actually are not the same thing.

• Semen is the grayish-white fluid produced by the testes and ejaculated during orgasm.

• Sperm are the tadpole-shaped cells that are contained in and swim through semen.

• DNA is derived from sperm not from semen.


Value in CasesDeath• The victim’s body and clothing, as well as

bedding, towels, and other articles at the scene, may be sources of such stains.

• Other possible sources of such evidence are suspects and items in their surrounding environments, such as clothing, bedding, and their automobiles.


Value in CasesRape and Other Sex Offenses • Semen and sperm are often, although by no

means always, found as physical evidence in sex offenses.

• Through DNA typing, it is possible to match semen stains (containing sperm) with a person’s blood sample or, in some cases, other biological specimens such as saliva, skin, or similar materials



Here are three main questions that laboratory examination of semen stains may answer:

1. Does the stain contain human semen?2. Can the blood group (A, B, O, AB) of the stain be

determined? If so, what is it?3. If a blood specimen from the suspect is

available, does it match the DNA present in the semen sample?


Hair as Evidence

• Can be used to identify both the sex and the race of a person.

• Hair cannot absolutely identify a particular individual, as a fingerprint can, scientific examination can fairly conclusively rule out a strand’s having come from a particular individual.


Value in Cases

Assault• Individual strands, clumps, or tufts of hair may

be grasped in the hand of a victim.• Microscopic examination of a hair may

suggest whether it has fallen out or has been forcibly pulled out.


Value in Cases

• Rape– Pubic hairs

• Hit-and-Run– When a vehicle strikes a person, hairs and fibers

often become embedded in areas of fresh damage.

• Upon Death– Collect a sample of about 20 strands of hair from

the deceased in all cases of sudden or unusual death.



• Is the hair sample human or animal?• If human, from which part of the body did it

originate?• If animal, what type of animal was it (dog, cat,

deer, wolf)?• Are there any indications of the characteristics

of the individual from whom it came?



• Could the hair have come from a particular person? If so, what is the probability that it did come from that person?

• Did the hair fall out naturally, was it pulled out, or was it cut by a sharp instrument?

• Are there any foreign substances adhering to the hair such as dye, blood, or grease?


Fibers as Evidence• Fibers are present in crime scenes more

frequently than any other type of microscopic evidence.

• Adhesive-tape technique – A method of collecting microscopic

evidence in which transparent tape is used to cover an area to which physical evidence such as fibers may be present

– When the tape is pulled off, the evidence adheres to the sticky surface of the tape.


Fibers as Evidence

Fibers can be classified into two major groups: Naturally occurring Manufactured


Fibers as Evidence• Naturally occurring fibers

– Derived from various vegetative and animal sources and used in manufacturing cords, ropes, linens, and clothing.

• Manufactured fibers – Comprised of two subgroups:

• Regenerated and synthetic fibers.• Regenerated fibers are made from natural materials

processed from the cellulose in cotton and wood pulp.– Synthetic fibers are produced entirely from

chemicals.


Fiber Analysis• Fibers can be better sources of evidence and

information than hairs found at a crime scene because fibers are more distinguishable than human hair.– uniformity of thickness of strands– Actual number of microscopic fibers in every strand– color or dye origins– lengthwise striations– direction of fiber twists


Value in Cases• Assault

– Clothing fibers may be transferred between victim and suspect.

• Burglary– Fibers may snag at the point of entry.

• Death– Transferred between the victim and the assailant.

• Rape– Articles such as bedding, automobile seat covers, or

furniture.



What type of fiber is the sample? Is the same type of fiber present in samples of the

victim’s and suspect’s clothing? Does the sample exactly match when compared with

a standard sample taken from the victim’s or the suspect’s clothing?

Is it the exact shade of color as the standard? Are there any points of similarity?


Glass as Evidence

• Many different formulas are used to manufacture glass, and the variations in density, refractive index, and light dispersion give glass a very high value as evidence.

• Very tiny shards of glass sometimes adhere to a suspect’s shoes, clothing, hair, or skin


Glass as Evidence• Radial fractures

– Cracks that start at the center of the point of impact where an object strikes a pane of glass and radiate outward, creating a slightly star-shaped pattern.

• Concentric fractures – Irregular, but concentric

circular crack patterns in the broken glass around the point of impact.


Glass as Evidence

•Conchoidal fractures –Provides information about the direction of the force that broke the glass because glass breaks first on the side opposite to the force applied to it.


Value in Cases• Burglary

– Burglars often break a window or door to quickly escape the crime scene.

– Any person standing close to glass when it is broken invariably picks up fragments on his or her clothing.

– In cases where windows have been broken, the clothing of burglary suspects will often carry microscopic glass fragments.

• Hit-and-Run– In a hit-and-run accident, a headlight is often broken.– Less common, but also possible, is a broken windshield.– The scene of the accident, the vehicle, and the clothing of

the victim can all be sources of glass fragments.



From a laboratory examination of glass, the following questions may be answered:

1. If a window was struck by a blunt instrument, such as a rock, stick, or fist, from which side was it struck?

2. If a window was struck by a bullet, from which side was it fired?

3. If two or more bullets were fired, is it possible to determine the sequence of firing?

4. Can the composition of the window glass be matched to known comparison specimens?

5. Can the refractive index of the glass sample be used to match the sample with known comparison specimens?


Paint as Evidence

Paint can occur as physical evidence in three different forms:

Chips or flakes, as may be found adhering to clothing

Smears, from either fresh paint or old “chalking” paint

Intact finishes, on objects such as tools or automobiles at the crime scene


Value in Cases• Burglary

– Paint fragments, often microscopic, may be found on the clothing of a suspect, on the tools used to commit a burglary, or in a vehicle.

• Hit-and-Run – The clothing of the victim, upon microscopic examination,

will often yield minute paint fragments resulting from impact with the vehicle.

– In collisions between vehicles, a considerable amount of paint will invariably be interchanged.



Can the flakes of paint be fit together along a common fracture to provide a conclusive identification of the paint’s source?

Can the source of the paint be identified with a high degree of probability if both the sample and the comparison specimen contain identical layers or components?

Is it possible to establish the color, year, and make of an American-made or imported vehicle from a paint chip?


Firearms/Ammunition as Evidence

• Firearms evidence is common at many crime scenes.

• The evidence may reveal a fingerprint or have blood, hair, or fibers adhering to them.


Firearms/Ammunition as Evidence

• Question to be answered:– Was a particular bullet fired from a specific gun?

• Bore – The opening in the barrel of a gun or rifle.

• Striations – Marks and lines or scratches

on the sides of a bullet made as the bullet passes through the rifled bore of a weapon.


Additional Information from Bulletsand Cartridges

• Fired bullets typically experience some degree of damage or fragmentation.

• Cartridge – The casing that holds the bullet (projectile), gunpowder, and

primer together as a single unit.• Firing pin impressions.• Marks also may be left on the cartridge by the gun

when it ejected the cartridge after it was fired.


Value in Cases From what type or make of firearm

was the fatal bullet fired? Was the fatal bullet fired from the

suspect’s gun? Was the discharged cartridge case

fired from the suspect’s gun? Were two or more bullets fired from

the same gun? Were two or more cartridge cases

fired from the same gun? What was the gauge of the shotgun

used? What size shot was used?


Value in Cases What was the composition of the shot used (lead or steel)? How far from the victim was the gun held? Is there any foreign material attached to the bullet that

would indicate its path or flight? Was this gun carried in the suspect’s pocket? What were the serial numbers that might have been ground

off this gun? Has the gun ever been used to commit an offense, not yet

solved, in which bullets or cartridges were previously submitted?

Are there any identifiable fingerprints on either the weapon or the cartridges or shells?


Drugs as Evidence

• Drugs may be found concealed in objects or on individuals, and occasionally in balloons inside of individuals, or lying in plain sight.

• Field drug identification kits.• Full analysis of suspicious substances must be

undertaken at a laboratory.


Value in Cases

• Assault– it is possible that vials or packages of drugs may be lost or

dropped during the struggle.

• Death– Drugs may have been used by either the victim or the

suspect or may have been a contributing factor in the homicide.

• Illegal Drug Laboratories– Until analyzed, all substances found in such crime scenes

should be considered highly toxic and dangerous.


Possible Examination Results1. Confirm corpus delicti.• Laboratory analysis can establish what the powder or other substance

found at the crime scene actually is.• In many cases, such analysis is necessary to determine that an illegal

act has occurred.2. Identify designer drugs. • So-called designer drugs involve modifications of controlled substances

that alter the chemical structure to the point where it may no longer be identified as an illegal and regulated substance.

• Nonetheless, the modified drug may still possess all of the original drug’s effects on the mind or behavior.

3. Quantify the amounts of illegal drugs. • Tests can determine the total weight and quantitative analysis of the

illegal drugs.• The quantity of a particular drug may alter the specific charge brought

against a suspect (personal consumption, distribution, or manufacturing).


Documents as Evidence

• Handwriting or typefaces may be compared with other written or printed materials to establish their identity.

• Documents may contain watermarks or special imprints that can help an investigator identify a distribution or manufacturing source.


Value in Cases• A document is anything on which a mark has been

made to convey some message.• Any form of document may be useful to investigators

in establishing whether a crime has been committed.• Identity Theft

– Identity thefts frequently require the criminal to create or misuse an assortment of documents including:

• checks• credit card applications and forms• mortgage applications• drivers’ licenses• birth certificates• an array of other documents


Value in Cases

• Suicide– Suicide note.

• Forgeries– Examination of a document may determine

whether the forger simulated the signature, copied it, or had no knowledge of the way the genuine signature looked.


Comparison Specimens of Documents

The Handbook of Forensic Science lists fourteen types of documents and writing implements that might be examined:1 handwriting (script)2 hand printing or lettering3 forgeries4 typewriting5 photocopies6 mechanical impressions (from printers, check writers,

rubber stamps, embossers, and seals)7 altered or obliterated writing


Comparison Specimens of Documents8 carbon paper9 writing instruments

pencils, pens, crayons, and markers10 burned or charred paper11 typewriters

brand identification from typewriting12 printers

brand identification from printout13 facsimile machines

brand name identification from sample14 paper

watermark and safety paper identification


Typewriter Comparison Specimens

• As with any mechanical device, the repeated use of a typewriter will result in wear and damage to the machine’s movable parts.

• To make a comparison, the investigator should type the specimen on paper similar to that of the questioned document.

• Remove the typewriter ribbon, and submit the ribbon and the typing specimens to the lab for examination.


Computer Printer Comparison Specimens

• Daisy-wheel technology• Dot matrix system• Laser and laser jet technology

– carbon powder or toner

• Modern printers--like their earlier typewriter predecessors--develop individualized flaws in the way they imprint characters.



Was a particular document written by a particular individual?

Is a particular writing forged? What was the make, model, and approximate age of the

typewriter or printer used? Was a particular typewriter used to type a particular

document? Was a particular check protector used to make a

particular imprint? What was the content of an erased, obliterated, altered,

or written-over writing, typing, or printing? What differences, if any, are there between inks in one or

several documents?


Possible Examination Results Which stroke was written last when two strokes of writing

cross one another? Did two pieces of paper come from the same source? Do uneven edges of torn paper match, proving that several

pieces originally formed the whole document? Do the perforated edges of a check, receipt, or stamp match

the corresponding checkbook, receipt book, or sheet or book of stamps?

Will the creases and folds in the document aid in determining where it has been—for example, in a particular billfold?

What is the context of writing or printing on burned or charred paper?


Flammables as Evidence

• Gas chromatography is the most effective way to detect and characterize flammable residues.

• Most arsons are started using petroleum distillates such as gasoline or kerosene.


Value in Cases

• Arson– The most common liquids encountered are:

• Gasoline• Kerosene• paint thinner

• Theft– The siphoning of gasoline from automobiles and the

theft of petroleum products from storage locations are examples of cases in which flammables may be significant physical evidence.


Possible Examination Results1. Confirm corpus delicti.

– The laboratory can isolate the flammable liquid from the fire debris and determine whether it is gasoline, kerosene, or a more exotic flammable

– Such examination can furnish evidence from which the jury may infer that the fire was intentionally set.

2. Connect flammables with a source available to the suspect. – If the liquid has not evaporated appreciably (for example, if it

is present in a can left at the scene or is well soaked into an unburned material), the laboratory can compare it with material available to the suspect

– The liquid might come from a drum of paint thinner.


Corrosives as Evidence

• Liquids such as acids and alkalies require special handling and containers.

• Consult and follow the advice of a laboratory expert before handling, preparing, or transporting any such liquids.


Explosives as Evidence

• Do not try to disarm, move, or transport explosive materials unless directed to do so by explosives experts.

physical evidence chapter 4. ©2008 the mcgraw-hill companies, inc. all rights reserved. the crime...

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