Crime Scene Investigation: How It's Done

The crime scene is documented to record conditions such as whether lights were on or off, the position of shades and doors, position of movable furniture, any ... HowIt’sDone SamplesThatMaybeCollectedataCrimeScene Awidevarietyofphysicalevidencecanbecollectedatascenethatisdeemedvaluable(“probative”)forcollectionandinvestigation: biologicalevidence(e.g.,blood,bodyfluids,hairandothertissues) latentprintevidence(e.g.,fingerprints,palmprints,footprints) footwearandtiretrackevidence traceevidence(e.g.,fibers,soil,vegetation,glassfragments) digitalevidence(e.g.,cellphonerecords,Internetlogs,emailmessages) toolandtoolmarkevidence drugevidence firearmevidence Thetypeofevidencecollectedwillvarywiththetypeofcrime.Inthecaseofaburglary,forexample,itwouldbecommontoperformtasksintheorderlistedbelow.Thiswillhelpensurethatevidenceisn’tinadvertentlydamagedordestroyed: Photographanddocumentthescene Collecttracematerials(especiallyfromprobablepointsofentry) Collectlow-levelDNAevidencebyswabbingareasoflikelycontact Collectotheritemsthatmaycontainbiologicalevidence Locateandcollectlatentfingerprints WhoExaminesCrimeScenes Thenumberandtypeofprofessional(s)responsibleforinvestigatingasceneandcollectingevidencelargelydependsonthetypeofcrimeandtheresourcesofthelawenforcementagency.Largeragenciesoftenhavededicated,highlytrainedcrimescenespecialists,whilesmalleragenciesmayrequirethatfirstrespondersordetectivesprocessthesceneinadditiontotheirotherduties. Inmanyinstances,acasewillbeinvestigatedbyadetectivewhoisresponsibleforinterviewingpersonsofinterestandvictims,pursuingleadsandpiecingtogethertheinformationthatisdevelopedfromthematerialscollectedatthescene.Thedetectiveworksintandemwithateamofcrimescenepersonnelwhosearchthesceneandcollecttheevidence.Thecrimesceneinvestigationteammayconsistofcrimescenephotographersandevidencecollectionpersonnelspecializingingatheringspecificevidencesuchaslatentprints,DNA,traceevidenceandthelike. IntheUnitedStates,therearenonationalrequirementsthatmustbemettoserveasacrimesceneinvestigator;however,investigatorscanachievefourlevelsofcertificationthroughtheInternationalAssociationforIdentification(IAI)thatdemonstratetheirproficiency: CertifiedCrimeSceneInvestigator CertifiedCrimeSceneAnalyst CertifiedCrimeSceneReconstructionist CertifiedSeniorCrimeSceneAnalyst OthercertificationscommonlyachievedincludetheEvidencePhotographerCertificationfromtheEvidencePhotographersInternationalCouncil,Inc.andBoardCertifiedMedicolegalDeathInvestigatoroftheAmericanBoardofMedicolegalDeathInvestigators(ABMDI). HowaCrimeSceneInvestigationisConducted Thecircumstancesthatinvestigatorsencounteratthescenewilllargelydictatetheapproachusedtoprocessthescene.Ahomicidewilllikelyrequiredifferenttreatmentandprocessingthanaburglary.However,toensureathoroughprocess,thesevenstepsoutlinedbelowareoftenfollowed.Thesestepscanbeconductedinadifferentorder,combinedorevenskippedaltogethertomeettheneedsofthesituation. 1.Establishthescenedimensionsandidentifypotentialsafetyandhealthhazards-Investigatorsinitiallylocatethe“focalpoint”ofthescene,themainareaofdisturbance.Thiscouldbearansackedbedroom,theareawhereanattackoccurred,ortheroominwhichavictimwasfound.Radiatingoutfromthatpoint,investigatorsestablishanareathatissizeableenoughtolikelycontainallrelevantphysicalevidencethatmaybepresent.Itiseasierforinvestigatorstocondensethesizeofasceneatalaterpointthantodiscoverthatsensitiveevidenceoutsidethescenehasbeendamagedordestroyedbyotherresponders,mediaoronlookers.Inaddition,potentialpathsofperpetratorentry/exitareidentified.Safetyisofparamountimportanceduringtheinitialapproachtothescene.Weapons,biohazards,chemicalhazardsandevenintentionaltrapscouldbewaitingforresponders.Ifmedical,fireorcoronerswillbeonscene,theywillneedtobeadvisedregardingevidentiaryissuesaswell. 2.Establishsecurity-AccordingtoLocard’sExchangePrinciple,everypersonwhoentersorexitsthescenewilladdorsubtractmaterialfromthecrimescene,soit’scrucialtoquicklysecurethearea.Tocontrolaccess,thescenemaybecordonedoffwithyellowcrimescenetape,conesorbyothermeans.Inaddition,acommonentrywayisoftenestablishedthatallcrimescenepersonnelwillusetoenterandexitthesceneandallpeopleenteringorleavingthescenearedocumentedoncetheboundarieshavebeenestablished.Additionalareasforconsultationandevidencestoragemayalsobeestablishedifnecessary. 3.Plan,communicateandcoordinate-Beforecollectingevidence,investigatorsmustfirstdevelopatheoryregardingthetypeofoffensethatoccurred.Knowingthetypeofcrimewillhelpinvestigatorsanticipatetheevidencethatcouldbepresent.Thismayrequiregatheringinformationfromwitnessesorpersonsofinterest.Basedonthisinformation,thecrimesceneteamwilldevelopanevidence-collectionstrategytakingintoconsiderationweatherconditions,timeofdayandotherfactors.Additionalforensicresourcesmayalsoberequestedtohandlespecialsituations. 4.Conductaprimarysurvey/walkthrough-Aninitialsurveyofthesceneisthenconductedtoprioritizeevidencecollection.Duringthiswalkthrough,theleadinvestigatorwillidentifypotentiallyvaluableevidence,takenotesandcaptureinitialphotographsofthesceneandtheevidence.Thecrimesceneisdocumentedtorecordconditionssuchaswhetherlightswereonoroff,thepositionofshadesanddoors,positionofmovablefurniture,anysmellspresent,thetemperatureofthescene,etc.Tofacilitatethisprocess,crimescenespecialistsmaycreateanevidence-freepathwayleadingtotheprimaryareaofinterestbyconductingathoroughsweepforevidenceinthatarea. 5.Documentandprocessthescene-Withaplaninplace,thecrimesceneteamconductsathorough,coordinatedinvestigationofthescene,collectingallprobativeevidence.Thisentailsdetaileddocumentationwithdigitalandvideocamerasor,ifavailable,a3-Dscanner.Forsomesituations,sketchesanddiagramsarealsocreated.Duringtheevidence-collectionprocess,itiscrucialthatthecrimesceneinvestigatorfollowproperproceduresforcollecting,packagingandpreservingtheevidence,especiallyifitisofabiologicalnature.Biologicalevidencecanbedestroyedordamagedbyweatherconditions,individualscaninadvertentlycontaminateit,oritcanbeoverlookedentirelyifalternatelightsourcesarenotusedtoinspectthescene. 6.Conductasecondarysurvey/review-Toensurethatthescenehasbeenthoroughlysearched,asecondsurveyoftheareaisconductedasaqualitycontrolstep. 7.Recordandpreserveevidence-Tomakecertainthatallevidenceisaccountedfor,aninventorylogiscreated.Thedescriptionsrecordedintothelogmustmatchthephotooftheevidencetakenatthesceneandthedescriptionincludedinthecrimescenereport.Forinstance,ifaguniscollected,theserialnumberofthefirearmintheevidencelogmustmatchtheserialnumbershowninthephotothatwastakenatthescene.Thispapertrailestablishesthechainofcustodythatwillfollowtheevidencethroughoutthelifecycleofthecase. HowandWhereTestsontheEvidenceareConducted Themostprobativeevidencewillbesenttoeitheraforensiclaboratoryor,ifthelaboratorydoesnothaveanexpertinthatforensicdiscipline,toanoutsideanalystforexamination.Tohelpidentifytheevidencethatismostvaluable,thecrimescenepersonnelmayconductinitialscreeningtests,calledpresumptivetests,atthescene.Thesetestscanbeusefulindeterminingthetypeofsubstancepresent—whetherit’satoxinoradrug,astainthatcontainsbodyfluids,orevenwhetheradriedredsubstancefoundinthekitchenisbloodorketchup. Presumptivetestsallowinvestigatorstonarrowthefieldofpossibilitiestoacertainclassofsubstance,buttheyarenotspecificenoughtoconfirmthepresenceofspecificcompounds.Inadditiontohelpingprovidecluestoindicatehowthecrimeoccurredandwhomayhavebeeninvolved,presumptivetestscanalsohelpreducethequantityofevidencethatissubmittedtothelabtoincludeonlythemostimportantitems.Thishelpstoexpediteprocessingatthelaboratory. Astechnologyadvancesanddevicesbecomemoreportableandaffordable,additionaltestingofevidencewilllikelybeconductedatthescene. Backtotopofpage▲ FindOutMore Introduction Principles Applications HowIt’sDone ◀ FAQs CommonTerms Resources&References