Forensic Science

T. Trimpe 2006 http://sciencespot.net

CRIMESCENE:Anyphysicallocationinwhichacrimehasoccurred

orissuspectedofhavingoccurred.PRIMARYCRIMESCENE: Theoriginallocationofacrimeoraccident.

SECONDARYCRIMESCENE:Analternatelocationwhereadditionalevidencemaybefound.

Crime Scene Vocabulary CrimeSceneVocabulary

ALIBI:Statementofwhereasuspectwasatthetimeofacrime.

ACCOMPLICE:Second(ormore)personassociatedwithsomeonesuspectedofcommittingacrime.

CrimeSceneVocabulary

Testimonialevidencewouldbeanywitnessedaccountsofanincidentorcrime.Itincludesoralorwrittenstatementsgiventopoliceaswellascourttestimonybypeoplewhowitnessedanevent.

Physicalevidencereferstoanymaterialitemsthatwouldbepresentatthecrimescene,onthevictims,orfoundinasuspect’spossession.

Traceevidencereferstophysicalevidencethatisfoundinsmallbutmeasurableamounts,suchasstrandsofhair,fibers,orskincells.

TypesofEvidence

Source:http://www3.sc.maricopa.edu/ajs/crime_scene_technician.htm

Whatwillevidencecollectedatascenedofortheinvestigation?

•  Mayprovethatacrimehasbeencommitted•  Establishkeyelementsofacrime•  Linkasuspectwithacrimesceneoravictim•  Establishtheidentityofavictimorsuspect•  Corroborateverbalwitnesstestimony•  Exoneratetheinnocent.•  Givedetectivesleadstoworkwithinthecase

TypesofEvidence

POLICEOFFICERSaretypicallythefirsttoarriveatacrimescene.Theyareresponsibleforsecuringthescenesonoevidenceisdestroyedanddetainingpersonsofinterestinthecrime.TheCSIUNITdocumentsthecrimesceneindetailandcollectsanyphysicalevidence.TheDISTRICTATTORNEYisoftenpresenttohelpdetermineifanysearchwarrantsarerequiredtoproceedandobtainsthosewarrantsfromajudge.

CrimeScenePersonnel

TheMEDICALEXAMINER(ifahomicide)mayormaynotbepresenttodetermineapreliminarycauseofdeath.SPECIALISTS(forensicentomologists,anthropologists,psychologists,etc)maybecallediniftheevidencerequiresexpertanalysis.POLICEDETECTIVESinterviewwitnessesandconsultwiththeCSIunit.Theyinvestigatethecrimebyfollowingleadsprovidedbywitnessesandphysicalevidence.

CrimeScenePersonnel

Step1:InterviewThe first step in investigating a crime scene is tointerview the first officer at the scene or thevictim to determine what allegedly happened,what crime took place, and how was the crimecommitted.

Thisinformationmaynotbefactualinformationbutitwillgivetheinvestigatorsaplacetostart.

CrimeSceneProtocol

Step2:ExamineThe second step in the investigation of a crimescene,whichwillhelp identifypossibleevidence,identify thepointofentryandpointofexit, andoutlinethegenerallayoutofthecrimescene.

CrimeSceneProtocol

Step3:DocumentThe third step in the protocol involves creating apictorial record of the scene as well as a roughsketch to demonstrate the layout of the crimescene and to identify the exact position of thedeceased victim or other evidence within thecrimescene.

CrimeSceneProtocol

Step4:ProcessThisisthelaststepintheprotocol.The crime scene technician will process the crimesceneforevidence,bothphysicalandtestimonialevidence.

It is the crime scene technicians responsibility toidentify, evaluate and collect physical evidencefrom the crime scene for further analysis by acrimelaboratory.

CrimeSceneProtocol

MoreVocabulary

SUSPECT:Personthoughttobecapableofcommittingacrime.

DrugChemistry –Determines thepresenceof controlledsubstancesandtheidentificationofmarijuanaTrace Chemistry - Identification and comparison ofmaterialsfromfires,explosions,paints,andglass.Microscopy – Microscopic identification and comparisonof evidence, such as hairs, fibers, woods, soils, buildingmaterials,insulationandothermaterials.Biology/DNA – Analysis of body fluids and dried stainssuchasblood,andsaliva.Toxicology – Tests body fluids and tissues to determinethepresenceofdrugsandpoisons.

InvestigatingtheEvidence

Source:http://www.isp.state.il.us/forensics/

LatentPrints-Identificationandcomparisonoffingerprintsorotherhiddenimpressionsfromsourceslikefeet,shoes,ears,lipsorthetreadonvehicletires.Ballistics(Firearms)–Studyofbulletsandammunitionthroughthecomparisonoffiredbullets,cartridges,guns,andgunpowderpatternsonpeopleandobjects.Toolmarks–Examinesmarksleftbytoolsonobjectsatacrimesceneoronavictim,suchasahammerusedtobreakadoororascrewdriverusedtopickalock.QuestionedDocuments-Examinationofdocumentstocomparehandwriting,ink,paper,writinginstruments,printers,etc.,thatwouldhelptoidentifyitsorigin.

InvestigatingtheEvidence

Mock Crime Scene: http://www.masss.gov

In this made up crime scene, what evidence would you collect?

Let the evidence speak for itself.

Presentation developed by T. Trimpe 2006 http://sciencespot.net/

Locard’sExchangePrinciple

"EveryContactLeavesaTrace"Thevalueoftrace(orcontact)forensicevidencewasfirstrecognizedbyEdmundLocardin1910.Hewasthedirectoroftheveryfirstcrimelaboratoryinexistence,locatedinLyon,France.TheLocard’sExchangePrinciplestatesthat:"withcontactbetweentwoitems,therewillbeanexchange."Forexample,burglarswillleavetracesoftheirpresencebehindandwillalsotaketraceswiththem.Theymayleavehairsfromtheirbodyorfibersfromtheirclothingbehindandtheymaytakecarpetfibersawaywiththem.

EvidenceExamplesPaint•  Physicalandchemicalanalysisofpaintevidence(chips

orresidue)canindicateit’sclass,suchasautomobilepaint,housepaint,nailpolish,etc.

•  Theevidencecanbecomparedto40,000different

typesofpaintclassifiedinadatabase,whichcanbeusedtoidentifyaparticularmakeormodelofcarorbrandoftool.

CSIPaintAnalysis

EvidenceExamples

Didyouknow?Mostpaintevidencesubmittedtoalabwillcomefromhit-and-runcasesinvolvingautomobiles.

Paint

• Paintevidencecanalsoindicateindividualcharacteristicsifaninvestigatorisabletofindsimilaritiesbetweentwosamples,suchasthecolor,numberoflayers,chemicalcomposition,oraphysicalmatchbetweentheedgesoftwopaintchips–onefromatoolandonefromacrimescene.

PaintLayers PhysicalMatchofPaintChipEdges

PaintTransferonaCar

CSIPaintAnalysis

Glass

•  Glass particles can be found at various crime scenes,suchasbreakingandentering,hitandrun,vandalism,ormurder.

•  Glass at a crime scene is analyzed to determine itscolor, surface characteristics, tint, thickness, density,chemicalcomposition,andrefractiveindex(RI).

CSIGlassAnalysis

Glass

Theresultsofthetestsprovidecluesaboutthecrimeandhelp investigators connect the evidence to a suspect orotherobjectusedinacrime,suchasmatchingglassfromacrimescenetoaheadlighttoasuspect’scar.

Thepatternofcracksinawindshieldfracturecanrevealinformationaboutspeed,occupantposition,andangleofimpact.

Magnifiedimageofglassfragments

CSI Glass Analysis

Explosives•  Explosivesubstancescanbeexaminedtodetermine its

chemical composition to identify the type of explosiveusedanditsorigin.

•  Tracesofexplosivesfoundonasuspect’sclothing,skin,hair, or other objects may be matched to explosivesfromthecrimescene.

CSI&Explosives

Explosives

•  Materials used to make an explosive device will becompared to evidence found in the suspect’spossessiontoconfirmamatch.

CSI&Explosives

Ballistics

•  Characteristics of ammunition, firearms, and residueare examined to find matches between suspects andtheevidencefoundatacrimescene.

•  Chemicaltestscanrevealgunshotresidue(GSR)onthehands, face, or clothing of a victim or suspect toindicatehowcloseapersonwastoafiredgun.

Learn more about ballistics …

Did you know? Caliber (handguns & rifles) or gauge (shotguns) refers to the size of the internal diameter of a gun’s barrel.

Ballistics

•  Rifling (grooves) in a gun barrel causes distinctivegrooves,indentationsandscratchesuponfiredbullets,whichcanbematchedtotheweaponthatfiredthem.

•  Police are able to search the Integrated BallisticsIdentification System (IBIS) database to comparemarkings from bullets, cartridge cases, and shotgunshellstoballisticevidence.

Investigatorscancomparethestriationsonbulletsto

seeiftheymatch.

Dust&Dirt

•  Dust,dirt,orsandevidencecanrevealwhereapersonhastraveledandmaybepickedupatacrimesceneorleftbehind.

•  Investigatorsexaminethesamplesforchemicalcomposition,pollen,plantmaterial,andotherorganicmattertofindlinkstoaspecificcrimescene.

Microscopic Image of Sand

Fingerprints

•  Thereare3typesoffingerprintpatterns:arches,loops,andwhorls.Investigatorsalsoidentifyuniqueridgecharacteristicsinafingerprintthatcanbeusedtoidentifyasuspectorvictim.

•  AFIS(AutomatedFingerprintIdentificationSystem)is

adatabaseusedbyinvestigatorsatlocal,state,andnationallevelstosearchformatchestofingerprintsfoundatacrimescene.

ImpressionEvidence

Shoeprints&TireTracks•  Impressionevidencecanbephotographed,liftedwith

tape,orcastwithplastertocomparetoasuspect’sshoesortires.

•  Investigatorswillexaminetheevidencetoidentifythebrandofshoeortirebasedonitstreadpatternandotherphysicalfeaturestoprovideleadsinthecase.

Shoeprints&TireTracks•  Shoesandtireswillalsoshowwearpatternsafterbeing

usedforaperiodoftimeaswellasotherfeatures(scratches,nicks,andcuts)thatcanbeusedtomatchevidencetospecificitems.

•  Forexample,shoeprintscanbematchedtoasuspectbasedonhowthetreadsontheshoesthatareworndownduetothatperson’swalkingstyle.

BiteMarks•  Eachofthe32teethinhumansisuniqueduetoage

andwear.•  Impressionsandphotographsofbitemarksleftona

victim,assailant,orotherobjectatacrimescenecanoftenbematchedtodentalrecords.

ToolMarks•  Tinynicksandchipsformontheedgesofatoolasitis

used,whichcanbeusedtoidentifymatchesbetweenevidenceandsuspects.

•  Toolsmayalsopickuptracesofbloodorothersubstancesthatcanbetestedorhavefingerprintsthatcanbelifted.

FractureMatches

•  Whenanobjectbroken,torn,orcut,twouniqueedgesareformed,whicharereferredtoasfracturelines.

•  Theseedgescanbecomparedbythenakedeyeorwithmicroscopestoseeiftheyfittogether,whichindicatesthattheymayhavebeenpartofthesameobjectatonetime.

FractureMatches

•  Investigators may compare the edges on pieces oftape,glassfragments,paintchips,piecesofacarfromanaccident,paperbag,etc.tofindpossiblematches.

Wounds

•  Woundscanoftenbematchedtoweaponsortoolmarksontheweapon.

•  Investigatorsmayalsobeabletodeterminetheweapon'ssize,shape,andlength.

•  Analysisofawoundmayprovidescluestoavictim’sinjuries,characteristicsofthesuspect(left-handed,right-handed,height,etc.),andpositionsofthevictimandsuspectatthetimeoftheincident.

QuestionedDocuments

•  Examinerswillanalyzearansomnoteorotherdocumenttofindcluestolinkittoacrimesceneoraspecificsuspect.

•  Theywillanalyzethetypeofpaperused,printingmethodorhandwritingstyle,andtypeofink.

•  Otheruniquefeatures,suchas

watermarksonstationaryorindentationsmadeassomeonewroteonapageinanotebook,mayprovideusefulclues.

FBI Questioned Documents

UNIT

Insects

•  Flies,beetles,andotherinsectscanprovideusefulcluesaboutacorpse.

•  Forensicentomologistsusefactorssuchasweatherconditions,thelocationandconditionofthebody,andtheirknowledgeofthelifecyclesofinsectstohelpthemestimatethepostmortemintervalorPMI(thetimebetweendeathandthediscoveryofthebody).

DNA

•  InvestigatorscanextractDNAfromalmostanytissue,includinghair,fingernails,bones,teethandbodyfluids.TheDNAisusedtocreateaprofilethatcanbecomparedtoprofilesfromsuspectsorvictims.

•  CODIS(CombinedDNAIndexSystem)isadatabasemaintainedbytheFBIthatisusedtofindmatchestounknownDNAsamplesfromacrimescene.

SkeletalRemains

Forensicanthropologistsanalyzeskeletalremainstodeterminefourcharacteristicsforavictim:age,gender,race,andstature(height/build).

•  Gender–Determinedbyexaminingthepelvis,humerus,andfemur

•  Ageandstature–Determinedbyanalyzingthedevelopmentoftheteeth,bonegrowth,andthelengthofspecificbones,suchasthefemur.

•  Race–Determinedbyanalyzingtheskullforcharacteristicsthatarecommonamongpeopleofdifferentraces.

SkeletalRemains•  DNAsamplescanbecollectedfrom

bone,teeth,andhairtoprovidecluestoaperson’sidentity.

•  Scientistsmayalsobeabletogaincluesastoaperson’spast,recentinjuries,orthecauseofdeathbasedonbonefracturesandothersignsoftrauma.

WhatDoForensicAnthropologistsDo?

Generally,forensicanthropologistsDONOTdoanyofthefollowing:

•  Collecttraceevidence(hair,fibers)•  RunDNAtests•  Analyzeballisticsorweaponevidence•  Analyzebloodspatter•  Conductautopsies

WhatDoForensicAnthropologistsDo?

WhataforensicanthropologistDOEStoaidinacase:•  Goestoacrimescenetoassistinthecollectionofhumanremains

•  Cleansupthebonessothattheymaybelookedat•  Analyzesskeletalremainstoestablishtheprofileoftheindividual

•  Looksattraumaevidentonthebonestoestablishthepathwayofabulletorthenumberofstabwounds

•  Workswithaforensicodontologist(dentist)tomatchdentalrecords

•  Testifiesincourtabouttheidentityoftheindividualand/ortheinjuriesthatmightbeevidentintheskeleton

BodyFluids•  Blood,saliva,sweat,andurinecanbeanalyzedtogive

investigatorsinformationaboutthecrimeaswellasitsvictimorthesuspect.

•  Chemicalsandultravioletlightcanbeusedatacrimescenetofindbodyfluidevidence.

•  Areaswithpotentialevidenceareswabbed,baggedandcollectedinvials,whichareairtightandhavealowriskofcrosscontamination.

Examples:•  Vomitandurinecanbeused

totestforalcohol,drugs,andpoisons.

•  Cigarettebuttsmaycontaindriedsaliva.

•  BloodcanprovideDNAevidenceandbloodspattercanprovidecluesaboutthecrime.

BodyFluids

Hairs&Fibers•  Hairsandfibersmaybetransferredfromthesuspector

thesuspect’sclothestothevictims’andviceversa.

•  Forexample,asuspectmaypickupcarpetfibersonhisshoesorleavehairsbehindatacrimescene.

MicroscopicImageofHairs&Fibers

Hairs&Fibers•  Hairscanbeexaminedtoidentifytheirorigin,suchas

humanoranimal.HairswithrootsintactcanbetestedforDNA.

•  Fibersareusedtomakeclothing,carpeting,furniture,beds,andblankets.Theymaybenaturalfibersfromplantsoranimalsorsyntheticfibersthatareman-made.

MicroscopicImageofHairs&Fibers