The Biological Crime Scene It’s Not Just About DNA

Locard: "Every Contact Leaves a Trace".

Blood at the Scene is the most visible example of the Locard Exchange Principle

Think about the totality of evidence one might expect at a crime scene: impression evidence, bloodstains, bullets, etc. Trace evidence

All are important, Scene investigators often fail to find one or more, simply assuming not present.

Not unusual. It is expected because of the crime circumstances. Ballistics evidence is not expected and should not be present if the crime did not

involve a shooting. Failing to locate biological evidence, however, has a different “feel” because of the

lofty stature of DNA. BECAUSE it can identify someone. Crime scene investigators and scientists focus FIRST on finding biological

evidence, so much so that their rallying cry might well be, “Find DNA and you’ve got your perp.”

This works because DNA profiles from biological evidence collected at the crime scene are uploaded into an FBI maintained database –

CODIS (Combined DNA Indexing System). CODIS: Once in the system, scene profiles can be matched to other crime scenes, convicted felons, arrestees or to identify missing persons.

DNA is coveted as evidence from both investigational and legal perspectives.

Biological Evidence

At some scenes, investigators fail to find biological evidence.

It is probably safe to say that every crime scene involving people probably had biological evidence … means that investigators have been missing biological evidence for a long time.

Reality: In homicide cases: Only 5-10% yield of biological evidenceThe fact is, they missed it.

Consider this

Anyone entering a room brings something of themselves with them. When they leave the room, they leave something behind. Certainly, whatever is left behind might be difficult or even impossible to find.

But new technology on the nebulous horizon might be able to find it.

How Much Biological Evidence Is at a Crime Scene?

Example Case: Investigator finds young deceased

male on the floor. no head hair and a large contusion on the side of his head.

No obvious bloodstain impact spatter.

No apparent active bleeding: only a trickle of blood on the deceased’s cheek,

No blood droplets on the floor … no sign of a struggle.

Outside the back door on the pavement is an old, broken brick with rough edges. … Location is not particularly unusual … should not any raise suspicion that it might be the murder weapon.

Picking up the brick and casually examining it reveals nothing except, perhaps, some dirt: certainly no hair and there is no obvious blood or skin.

But this is the murder weapon AND biological evidence is present. By definition, biological evidence must be present. Many scene investigators will fail to collect the brick, and others might … just to be safe.

Both investigators might believe the brick holds no evidentiary value. The forensic scientist in the laboratory could have a different opinion based on finding shed skin cells lodged in the its crevices,

A technique that has not yet found its way into the field.

The message: Biological evidence is always

present. Unfortunately, we do not yet

have the technology to detect all of its traces

“Common Examples” … examples of forensically important biological evidence occur more than others.

Others also occur commonly … fingerprint residue or sloughed off cells … investigators do not think of them as common biological evidence;

Fingerprints: not thought of as biological evid

Sloughed-off Cells: not visible.

The reason is that the value of fingerprint residue is thought of in terms of its friction ridge detail.

Fingerprints contain biological substances, some of which has current or potential forensic value: fatty acids, proteins and cells (DNA).

Thinking of fingerprint residue a little differently may pave the way for it to become more valuable as an example of biological evidence.

Common ExamplesBlood – Human & Animal

SemenSalivaUrineFecesVomitHair

Fingerprint residueSloughed Off Cells

Not So Common ExamplesBacteria

Plant materialPollenViruses

What is Biological Evidence

Critical elements of the macro and micro scenes Bloodstain patterns, droplets, etc Pollen, bacteria, etc.

Arguably leader’s most important responsibility, given the critical importance of DNA, is to find and collect anything having biological properties. This is a top priority. Not an easy task:

Is it everywhere Represents only a small fraction of the totality of the biological spectrum

present. With the possible exception of a bio-terrorist event, the most probative biological

evidence comes from people. Who live where the crime occurred, visitors where the crime took place but had nothing to do with the event, public officials who investigate the scene and the criminal who commits the crime.

Challenge: Find important probative biological evidence among all present. Successful searching requires : All senses, ability to think creatively, common

sense … Luck, too.

Finding Biological Evidence

The successful search for biological evidence, any evidence for that matter, requires special attributes and diligence.

Acquiring the appropriate expertise is not a matter of attending a workshop that teaches how to use an ALS to locate evidence: semen, saliva or urine or how to employ presumptive chemical tests to classify an unknown stain as blood.

The Cognitive Tools The Evidence Analysis Cascade Your Brain Logical & Critical Thinking Experience Understanding the Science and Technology

The Intellectual Approach is the Key to Success Appropriate scientific education,

experience, Brains that think creatively and

skeptically, Understanding the underlying science

behind the technology and Being aware of and knowing how and

when to apply technology … the scene investigation is poised for disaster.

The investigator’s mission is “Never Miss Anything Probative”

Historically:Blood: Chemical tests commonplace 100 years ago to

determine whether reddish stains might be blood. Semen: In the 1950’s they used enzymatic tests (acid

phosphatase test) to determine whether a crusty stain might be semen.

Modern Techniques use technology High intensity light sources for the most part have

replaced touch for locating latent biological stains. The historical technological sequence started with UV lights followed by lasers and then alternate light sources (ALS).

ALS’s, make locating biological evidence easier, especially semen, saliva, urine and blood. Scene-forward immunological tests have entered the

forensic arena, which can confirm whether a stain is human blood, semen or even saliva.

Regardless of advances in technology, the most important tool the scene scientist possesses is the brain … critical thinking (the brain) marries technology.

Brain is best and only way to find biological evidence.

Locating Critical Biological Evidence

• Eye • Brain• Touch• Hi-Intensity light• ALS• Chemical Tests• Enzymatic Tests • Immunological

Tests

The Scene & the Forensic LaboratoryThe Evidence Analysis Cascade

Pattern Analysis

The Evidence Analysis Cascade

Trace Evidence

Presumptive TestingScrapping Tape lift

Gross Visual Examination

Tactile Analysis

Stereomicroscopy

Genetic Marker Testing

ImmunoChromat.

HairsFibers

Soil/Paint/Glass

Pattern Analysis

ImpressionEvidence

BiologicalEvidence

ChemicalTesting

EnzymeTesting

Confirmatory Testing

Species Testing

MicrocrystalAnalysis

ALS

Lectins

DNA

Confirmatory Testing

MicroscopyInstrumentalAnalysis

Immuno.Chromat.

Pattern Analysis

Red = Common TechniquesBlue = Lab only Techniques

Commonly Occurring Biological Evidence

Blood

Blood

Cells Liquid

Red Blood CellsWhite Blood Cells

Plasma Serum

What Is Blood?

Plasma Cells

Blood Complex Connective Tissue

SaltsBlood Group

Antigens

Antigens

Drugs

Hormones

Antibodies

DNA

HLA Antigens

Blood Group Substances

White Cells Red Cells

Enzymes

Isoenzymes

Genetic Markers

Individual Specific

Antibodies

Forensically Speaking: What is Blood?

Genetic Markers

Drugs of AbusePrescriptions

IdentificationPsychological Behavior

Disease Susceptibility

Individual Identity

Ancestry Sexing

Racial Identity

Forensically Critical Information from Blood

DNA Profiling

Antibody Profiling

Presumptive testing … A test helps an investigator decide whether a particular stain

MIGHT be blood and thus have investigative value. A presumptive test, then, is a “maybe” test, one where a positive

result means that the stain might be blood. These are not confirmation tests.

Other tests are needed to confirm whether the biological material is present.

On-scene testing for bloodCould It Be Blood?

The eye: Oldest presumptive test.

Not always red. o Dried blood can be red, brown, yellow, green or black, o Understanding the conditions under which these transitions occur is important.

The eye, not a stand-alone-instrument because connected to brain. Interprets color and then determines (presumptively) that red substance is blood. Evaluating it in the context of our experience, a

Experience is what is really what is being tested. Not a confirmatory test,

Coupling observational skills with experience narrows the range of possibilities. A good first approach, but technology can enhance the likelihood of finding blood.

Experiences are not infallible or applicable to all situations, and not the most reliable indicator of the ground truth. For an experienced scene investigator, observing something red having the appearance of

blood spatter means that it “looks like” blood. Does not mean that it is blood.

Certainly the investigator’s experience is important, but certainty is not the test of certitude.

Being “certain” that something is what one thinks it is does not make it so.

The Unaided Human Eye

Light enhances ability to “see” evidence where it normally would be invisible. Oblique lighting is an example of how light helps find impression evidence.

Flashlight is an important on-scene tool,

Recent developments in light technology – lasers and alternate light sources – have produced portable, high intensity instruments with tunable wavelengths that can highlight some categories of evidence better.

Useful example is ALS, which has proven to be a versatile resource for scene investigators because it enhances the ability of the human eye to “see” better.

The molecules that comprise the evidence absorb specific wavelengths of light. When this happens, the evidence will appear dark.

If the molecules lose energy, they might be seen as light – fluorescence. This is a topic we discussed in Part I of this lecture series. This happens because an ALS has a tunable wavelength dial that offers the scene scientist choices depending on the scene situation.

Tunable wavelengths are typically not available on a normal flashlight.

The Aided Human Eye – Alternate Light Sources (ALS)

Using Light SourcesTo Find Biological Evidence

The Electromagnetic Spectrum Using Light to Find Biological Evidence

190-290 290-400

Ultraviolet Region

Shortwave

Longwave

Visible Region

400-455 455-492

>700

492-577 577-597 597-622 622-700

Infrared Region

Violet Blue Green Yellow Orange Red

IR

Blood Absorbs LightAppears Dark

“Tricks”, depending on the surface on which the blood lies. For example, the 415nm (and 450nm) setting on the ALS (violet

light) makes the blood appear darker on light backgrounds, Enhances apparent visibility. Dried blood absorbs light at that 415nm,

o Why it appears darker instead of reddish or reddish brown. The increase in contrast between the blood and the surface forces

the eye into a more favorable region of the electromagnetic spectrum.

Detecting Blood with the ALSBlood on Light Colored Surfaces

Dark Surfaces 415nm approach does not work

Making the blood appear darker is counterproductive because the contrast between the surface and the blood is diminished

Difficult to see and easily missed, … forces scene investigators to choose alternative methods.

Subtract background: o Use light of different wavelengths (colors) … ALS. o If successful, blood will appear dark against a lighter background.

An example is blood on a red wall.

Oblique lighting on shiny surfaces

IR light

Blood on dark surfaces

Differentiating food from blood @ scene prevents the crime laboratory from having to analyze superfluous and irrelevant evidence.

Blood absorbs at 415nm … Does not fluoresce under long-wave

ultraviolet light (300-400nm – both settings on an ALS).

Tomato-based foods may or may not absorb light at 415nm (usually less so than blood) … Give blue-white fluorescence and a

yellow or yellow-orange fluorescence under long-wave UV light.

Blood Ketchup

Long-wave UV LightOn Wall

Stain on the left = bloodstain Stain on the right is a ketchup stain.

• The blood absorbs the light, which is why it appears darker.

• The ketchup has a blue-white fluorescence.

Differentiating Food Stains From Blood

Blood absorbs in the infrared, which makes it appear dark, Can visualize blood on dark backgrounds that do not absorb in IR Sometimes on dark, shiny surfaces.

In the past, o Delayed for film processing

Made on-scene usefulness problematic because it took time before the investigators knew whether the infrared light had “found” blood.

o Used show blood patterns on dark surfaces where it was known to be present.

o Not a mechanism for finding difficult to see bloodstains AT THE SCENE during the investigation.

Digital IR camera and the ALS are valuable on-scene partners Tools to help locate dried blood on difficult surfaces.

Digital cameras have characteristics different than film cameras simply because they the LCD viewers allow one to “see” the blood in-situ.

Infrared (IR) Cameras Combining Searching and Archiving

Instantaneous peek at dark surface … does not absorb IR light..

Camera expands an investigator’s sight range into the real-time near infrared, … IR digital camera is indispensible tool for on-scene investigations. Even when the ALS is of little or no help.

Importantly, too, the LCD IR image can be photographed and included in the crime scene unit’s case file.

Legend: White arrows point to bloodstains

The IR highlighted stain can be tested with presumptive chemicals or tested using immunochromatographic cards to ascertain whether it is blood or human blood respectively.

The stains on the carpet in photograph were invisible to the naked eye and to the settings on the ALS – the ALS could not effectively subtract out the background

Detecting Blood Using An IR Camera

ALS WavelengthsApplications to Finding Biological Evidence –

MiniScope 400

Bone 455/CSS/515 Orange OrangeTeethFingernails

Body Fluids CSS Orange 1-2 Orange Dk Surfaces UV Clear/Yellow None “ w/crust White/oblique Clear None

Evidence Type ALS Settings Goggle Camera Filter

Hair untreated Blk White/oblique Clear None treated-red/bld 415/CSS Yellow/Orange Yellow/Orange

Blood 415, 455 Clear/Yellow None

Choosing a Goggle ColorMatches Wavelengths

Color Range ALS Setting (nm) GoggleLong wave UV 300-400 ClearViolet 515-445 YellowBlue/green 455-515 OrangeGreen-red 536 Red - - - - - - CSS Orange

http://www.evidentcrimescene.com/cata/light/light.html

Detecting Blood @ the Scene

Chemical tests that react with blood were developed in the mid 19th century. Needed a method to know whether unknown stain might be blood Chemistry narrowed the range of possible substances by approximately 95%.

Positive chemical test means that there is approximately a 95% chance that the unknown stain is or contains blood.

Many reddish or dark stains at a crime scene are not blood. Example is stain from the spray of a shaken CokeTM can on a dark wall.

Each works on the same principle.

Two categories: Colored Dyes or Luminescence.

The former include a range of dyes that turn color in the presence of hemoglobin, a protein component of blood, and a peroxide – hydrogen peroxide is the most commonly used peroxide.

These reagents are available commercially and include a vast array of choices:

1862 Chemical Presumptive Testing

Common Presumptive Test Reagents

phenolphthalin (Kastle-Meyer)leucomalachite green (LMG)Luminol (BlueStar)3,3’,5,5’-Tetramethylbenzidine (TMB)leucocrystal violet (LCV)o-tolidineBenzidine: Carcinogenico-toluidinehydrogen peroxide: Bubbles

Blood – Presumptive testsGeneral Considerations

2H2O2

2O· + 2H2O

Heme Fe+++

Step 1: Oxygen free radicals cleaved from peroxide group

Heme Fe++

Free radical interacts

with organic chemicals (dyes)

O· chemical oxidized (Colored)

Presumptive test detects oxidized organic dyes

+ Chemical reduced

Step 2: Oxygen free radicals react with reduced dye

Kastle-Meyer TestCommonly Used Presumptive Test for Blood

P

CottonSwab

• Lightly moisten swab with distilled water– Ensure no excess of water

• Dissolve stain onto tip of swab• Add drop of ethanol• Add drop of KM reagent to stain

– color change at this point: false positive

• Add 3% H2O2

• Observe Pink Color– KM positive

One step All reagents added together

Considered to be most sensitive

Doesn’t allow for identifying false positives

Two Step Reagent added to the stain Peroxide added last

Three Step Alcohol added first Reagent second Peroxide last

Kastle-Meyer Test for BloodMost Common Lab & Scene Test

Also known as the phenolphthalein test

Other category are chemicals that react with hemoglobin and peroxide but instead of turning color, they luminesce: …

Chemiluminescence. Luminol, BlueStarTM and fluorescein, is used primarily at crime scenes

where clean-up is suspected. oLuminol and fluorescein have enjoyed a long forensic history, but

BlueStar is a recently available formulation for which claims of greater and longer luminescent intensity exist.

BlueStar … two formulations … one for on-scene use … training. Since the reagent is expensive, the training formulation is a less expensive version but its manufacturers warn it will destroy DNA.

The on-scene and more expensive version supposedly does not destroy DNA.

Luminescence produced can be dramatic

Blood Reacting Chemicals that Luminesce

BlueStarTM

The Luminol (BlueStar) Procedure Darken room or area as adequately as possible. Sometimes covering windows,

door areas, exit lights, etc, with black plastic bags will suffice.

Spray suspect area with 2% 5-sulfosalicylic acid and allow to dry. Sulfosalicylic acid fixes the proteins in blood by denaturing them

Set camera on tripod, set aperture to “bulb,” turn off lights and take photograph of scene using a 2 minute exposure. Check that photo is not over exposed. If over exposed, adjust shutter speed.

If exposure is adequate (see scene detail in photograph), trip shutter and spray area with BlueStarTM. Allow luminescence to develop.

When fluorescence begins to fade, spray the area again. Continue this process for the entire two minutes.

Then trip the shutter and observe the photograph.

Hemascein

Hemascein®, a non-luminol formulation, designed to Qualitatively reveal latent bloodstains at a crime scene.

How Hemascein WorksHemascein® detects latent bloodstains

using a novel fluorescein as active component

Area suspected of containing latent bloodstains sprayed with Hemascein® using ABASpray™.

Hemascein® reagent is reduced by hydrogen peroxide (colorless) and then oxidizes fluorescein.

Fluorescence comes after excitation an ALS Use ALS between 415 and 480 nm. After locating suspect blood, test for human origin

using immunochromatographic test. Evidence swabbed and transported for DNA analysis.

http://www.abacusdiagnostics.com/howitworks.htm

The choice of which to use and when is important.

Scene where an informant says that individual had been murdered years earlier.

Finding the blood visually or even with an ALS might be fruitless. Maybe the original scene had been remodeled or repainted. The team leader needs to decide how to approach the problem. After an exhaustive but unsuccessful search for visible blood, the team leader

might discuss the following with the team: Should spray using BlueStarTM ?

Can the team darken the room sufficiently? OR Should use a reagent that forms a color, such as leuco crystal violet OR

KM. Suppose investigation based on informant’s information that the room had,

been painted to hide blood, Consider possibility of finding the blood “under” the paint and discuss

how to accomplish that. One consideration is spraying with BlueStarTM.

So Many Choices: What to Use When?

Confirming Human Bood

Forensic application largely used to identify blood, semen, saliva and urine.

Can be conducted on-scene, BUT reagents must be purchased commercially, which raises the per/test cost significantly.

Not a presumptive test: Specifically identify unknown

stains as human blood Some cards cross react with

ferret blood, Semen or saliva (identify

salivary amylase). Tests purchased as testing kits,

Must pass quality tests for sensitivity and specificity.

Lateral Flow ImmunochromatographyRapid technique for identifying

small amounts of specific molecules.

http://www.creative-diagnostics.com/Colloidal-Gold-Lateral-Flow-Strips-Development.html?gclid=CMCC8-ry9LUCFY6e4Aod1lsA1Q

“Immunochromatography strip test, or namely lateral flow test, is a simple device intended to detect the presence or absence of the target analyte.” It’s a form of immunoassay. Well-known examples are in-home pregnancy tests.

Problem with immunochromatographic cards, especially those from Abacus and OTEB is that they suffer from what is known as the Hook Effect. Happens when testing overly concentrated samples of human blood

False negative test,o Incorrect and potentially misleading result obtained.o RSID cards do not demonstrate a Hook Effect

When the Hook Effect occurs, sample must be diluted and re-run. Quickness, ease-of-operation, specificity and sensitivity of these

immunochromatographic cards makes it tempting to avoid the traditional chemical tests entirely.

If cost is not an issue, this might be a best choice because these tests confirm the presence of human blood in a single test.

Used immune-card and/or stain extract can be submitted to the laboratory for DNA analysis, Should save the laboratory time in selecting certain scene stains from submitted

crime scene samples for DNA analysis, Laboratories normally prefer to extract the samples

Immunochromatographic Cards

Employing immunochromatographic cards exclusively Mistake, if all blood tested turns out to be

nonhuman. Negative test typically means that human blood is not

present. False negatives occur with highly concentrated

blood extracts … because of the Hook Effect. Exception is the blood test by RSID which has no

Hook effect. True negative occurs when there is insufficient

human blood present; all tests have limits of sensitivity.

Of the immuno-cards available, the Abacus Diagnostics card for blood is the more sensitive; HemaTraceTM card detects lower amounts of blood

than the RSID card. Investigators

Need to be aware of nuances among products Should test cards … for sensitivity and specificity

as part of the validation of a comprehensive quality assurance program.

Used with Permission from Dr. Reena RoyPenn State University

Immunochromatographic Cards

Touch DNACommon Buzzword in Modern Investigative Forensics

Cellular material is biological evidence with DNA. Perpetrator holds a weapon or picks up an object with

an ungloved hand, cellular material transfers from the hand to the object.

Much modern forensic DNA analysis involves what has become known as “touch evidence.” All biological evidence must be considered from the

perspective of its location at the scene, its pattern as well as its donor.

Touch DNA

Touch DNA is not Low Copy Number (LCN) DNA. LCN DNA profiling allows a very small amount of DNA to be analyzed, from as little as 5 to 20 cells.

Touch DNA testing involves analyzing “normal” amounts of DNA

Humans shed tens of thousands of skin cells each day, and these cells are transferred to every surface our skin contacts. When a crime is committed, if the perpetrator deposits a sufficient number of skin cells on an item at the scene, and that item is collected as possible evidence, touch DNA analysis may be able to link the perpetrator to the crime scene. Touch DNA has been successfully sampled from countless items including gun

grips, steering wheels, eating utensils, and luggage handles, just to name a few.

However, since Touch DNA is usually deposited in smaller amounts than the DNA found in bloodstains or other body fluids, it is more difficult to obtain DNA profiles from touch DNA samples. The key to obtaining successful Touch DNA results depends on recognizing items

which may be suitable for Touch DNA analysis and using the sampling technique that will recover the highest number of skin cells.

Touch DNA vs Low Copy Number (LCN) DNA

• Consider the potential evidentiary value of the DNA. Account for the relationship between the victim and

the suspect (if one exists), Consider any possibility of “innocent transfer” of

DNA that may have occurred before the alleged crime. If suspect is a family member, and either lived

with, or had recent contact with the victim, o Finding suspect’s DNA on the evidence may be

of limited probative value. Touch DNA can easily be transferred throughout the

household via day-to-day interactions, contact with furniture items/bedding, or through the laundry.

Touch DNA Potential Evidentiary Value

“Swabbing method”, Surface of item is rubbed with a cotton swab to collect possible cells.

This method preferred for hard items such as glass or plastic.

“Cutting method” Used for soft items, such as clothing, in which fabric from areas of interest is cut to collect

possible cells.

“Scraping” and “Tape Lift” methods Surface of soft items (such as clothing) are either scraped with a blade, or sampled with a

small piece of tape, to collect possible cells. Larger surface area can be sampled.

o An increase in surface area increases the number of possible cells recovered; therefore, increasing the chances of obtaining a DNA profile.

Ideal in situations where the scientist can locate areas on the item which are most likely to contain the perpetrator’s skin cells. o Clothing left at scene by the perpetrator

Pressure points on the clothing such as the interior neck of a shirt or the band inside a hat, are excellent candidates for these sampling methods.

Sexual assault case where victim’s clothing removed by the perpetrator, areas such as the waistband may contain sufficient cells belonging to the perpetrator to produce a profile.

Collection MethodsThinking Though Where The DNA Is

Provide lab scientist with case background information in order to receive the best advice on the potential value of DNA evidence

Crime scene photos can be quite useful. Lab scientist should have appropriate questions/suggestions for the investigator to

answer or consider.

Sexual assault by a stranger, finding the suspect’s DNA anywhere on the victim’s clothing may have evidentiary value.

Gather as much information from victim as possible (if living), Attempt to recreate the events if the victim is deceased.

If the victim’s pants pulled down, then the investigator and forensic scientist should consider sampling areas for Touch DNA where one would envision that the suspect would have grabbed during the assault. Finding the suspect’s DNA on the victim’s clothing, and in certain areas of the

clothing, may help corroborate the victim’s version of events and help address the allegations in ques tion.

Attempt to collect clothing of deceased individuals Collect samples from the clothing prior to the deceased being removed from the scene.

Collecting clothing at the scene PLUS optimal preservation allows obtaining Touch DNA at a later date, even if it’s not initially indicated to be present at the crime scene.

Thinking Through Evidence Collection

Channeling Information

Touch DNA sampling methods, and DNA processing procedures are very sensitive. Detecting contamination from law enforcement personnel or sampling investigator

Even when appropriate PPE is worn. May be necessary to obtain elimination samples from key personnel in the case where foreign DNA

profiles are obtained that cannot be attributed to a suspect or the victim. Also an increased chance of obtaining mixed DNA profiles containing DNA from individuals that

may have come into contact with the victim/evidence item near the time of the crime. Contributors to these mixtures could include the victim’s spouse or children

What does unexplained DNA mean? Foreign male profile from a Touch DNA sample may be obtained from evidence pertaining to a

female victim. If the male DNA profile doesn’t match the suspect in question the investigator needs to

consider its relevance to the case. The foreign profile could from the true perpetra tor and the original suspect could be innocent. DNA profile could be from adventitious transfer from crime scene personnel, first responders,

laboratory analysts, or crime scene equipment such as fingerprint brushes. Need to evaluate and address these questions before moving forward with the investigation.

Some evidence items are also not recommended for the collection. Severely degraded DNA - moldy clothing Samples exposed to extreme environmental conditions

Weapons left outside for months or years, have been washed, or are heavily soaked in the victim’s body fluids. Items likely touched by many people: public pay phone or store counter.

Limitations of Touch DNA

It is standard practice for crime scene personnel to wear Personal Protective Equipment (PPE) such as gloves, face masks, hair nets, and sometimes whole body suits.

When collecting potential Touch DNA items at a crime scene it is extremely important that as much PPE as possible is worn so as to limit the possibility of contamination via exposed skin, shed hairs, sweat, or saliva.

It is not uncommon to detect DNA profiles from Detectives, Paramedics, and Medical Examiners on evidence from cold cases and it is important that extra precautions be taken at the modern day crime scene.

J Assoc Crime Scene Reconstr. 2012:18(1)

Touch DNA Recommendations for the Crime Scene

Avoid speaking over evidence items (even if wearing a face mask). Collect evidence with disposable forceps (rather than gloved hands) Place each item in separate bag.Dust for prints using single-use brushes and small disposable ali quots of

powder To avoid cross-contamination.

Wet/dry swabbing method is commonly used at crime scenes. Be careful of scrape or tape lift methods because of increased probability

of contaminating the evidence/sample with ex ogenous DNA Increased potential for loss of the sample in an uncontrolled

scrapping. Also added risk of the investigator being cut by scalpel. Touch DNA items that may benefit from sampling with the scraping

or tape lift method should be collected and sent to the forensic laboratory to be sampled in a more sterile environment.

Scene Precautions for Collecting Touch DNA

Where to look for DNA Evidence

Source: https://www.ncjrs.gov/pdffiles1/nij/bc000614.pdf

Controlling Contamination

Control Contamination: Ensure scene safety and evidence integrity.

Limit scene access to people directly involved in processing Follow established scene entry/exit routes Designate a secure area for trash and equipment Use Personal Protective Equipment Clean or dispose of tools/equipment and PPE between

evidence collections and scenes Utilize single use equipment when collecting biological

samples

Personal Protective Equipment

Disposable glovesMasksEye protection

Provides a barrier to keep biological or chemical hazards from contacting the skin, eyes, and

mucous membranes and to avoid contamination of the crime scene

Swabbing for Touch DNA

Wear appropriate PPE Moisten swab with minimal

amount of distilled water (1 drop) Shake off excess

Swab the area Rotate swab to collect entire

surface Maximize swab coverage

Try not to re-use areas of swab

1 swab/area (6” of area)

Irregular or grained surfaces Swab with grain Move swab back & forth,

rotating swab surface so that new surface is continually collecting sample.

Resample area with dry swab Air dry all swabs Place swabs into appropriate

paper swab container

Bode SecurSwab™ DUO-V Swab System

DNA from Property CrimesGeneral Checklist

Identify visible stains first Easily Identify biological evidence. Will likely yield best results

Identify areas that may provide probative evidence when swabbing Areas not touched by victim Areas of forced entry

Identify items that were not at the scene prior to the crime Water bottles, cigarette butts, etc. that may have been left by the suspect

Gather elimination samples Victims, other residents/ users of the property (i.e. family/ roommates)

Collecting From Stains & Other Biological Sources

Cut stain and place into appropriate paper/cardboard evidence container

Crusty blood on various surfaces Swab or scrape

Swabo Moisten swab

appropriately (minimal amount of water and follow preceding instructions

Scrappingo Scrap with sterile

scalpel blade into paper fold (druggist’s fold)

o Include scalpel blade in packaging

o Scrape clean area of substrate as a control.

Bone, skin, teeth, nails Collect carefully & place in

paper/cardboard container Blood/sebum residue on glass

Check for ridge detail If present process as for

fingerprint enhancement/preservation

Joe Blozis: Evid. Tech. Mag. Sept/Oct 2012, pg 8-13.