An Introduction to Crime Scene Forensics

Philosophy and Practice

Crime scene investigation is a scientific AND an investigative endeavor

Success oExperienceoCreative thinkingoLogicoCorrect application of the science and the scientific method

Intensely intellectual exercise Bobby Jones - legendary golf pro

“Competitive golf is played mainly on a five-and-a-half-inch course...the space between your ears.”

A competent crime scene investigation is as cerebral an exercise as any scientific endeavor in forensic science, including forensic DNA analysis. Scene investigations are comprehensive, tedious and difficult scientific exercises that dovetail investigations and experience.

Philosophy

Police officers and scientists who investigate crime scenes are variably called crime scene investigators, forensic investigators or technicians depending on the jurisdiction in which they work.

Crime Scene TechnicianFor the discussions in this text, the term “crime scene technician” is neither

employed nor appropriate.

Scene investigator: A police officer/detective or other non-scientist working a scene.

Scene scientist: A scientist working at the scene is a scene scientist. May or may not be a scene

investigator. For these lectures, individuals who investigate crime scenes are considered collectively as scene scientists/investigators.

Terminology

Incorrectly consider crime scene investigation as a simple, non-scientific process, requiring minimal expertise that anyone can be trained to do Scene investigation is a matter of spreading dusting powder around;

shining an ALS or laser to find fingerprints, biological fluids and fibers; collecting the evidence; packaging it and delivering it to an appropriate location

It is WRONG

A Common Perception

✔ Balance of science and investigative activity required

to successfully work a crime scene

Crime Scene Investigation

A Scientific-Investigative Endeavor

Find evidence

Solve the crime Solve related crimes

Five reasons for investigating the crime scene Investigative leads for detectives Develop specific information Provide exculpatory evidence of innocence Accurate reconstruction Identify links to other crimes

Finding, packaging, preserving evidence are byproducts

Why Investigate the Crime Scene?

Who Should be Investigating Crime Scenes

Hypothetical Case

Police InvestigatorHighly Experienced Scene Investigator

Forensic Scientist (DNA or Trace Evidence Scientist)

CriminalistExperienced Scene Investigator

Who Would Want to Lead the Scene Investigation?

Your Brother Murdered @ home

Science Versus Practical Common Sense in Crime Detection, in 1931 Al Dunlap, then the editor of The Detective spoke at the 17th International Association of Identification (IAI) in Rochester, New York. At that convention, Captain Duncan Mathewson, the Chief of Detectives of the San Francisco Police Department said,

“Much has been said and published about the educated college policeman and detective and it is all bunk. Give me the practical detective with actual experience in handling criminals and criminal cases and with ten such men I will do more work than any college professor or so-called expert can do with one hundred of his trained nuts. Most of those that I have seen couldn’t put a harness on a mule, let alone catch a crook.”

Duncan continued, “There is an overabundance of self-styled scientific detectives and crime experts in this country. They would have a gullible public believe they are so scientific that the crooks would respond to engrave d invitations to visit police headquarters and surrender. Just how long the public will stand for this rot is a question.”

Dunlap concluded, “In truth, there is no real cause for a misunderstanding between the exponents of modern science and those who emphasize the need of practical common sense methods of crime detection. Science should simply confine its efforts to the solution of all problems that call for special scientific treatment, and never undertake to steal the show, so to speak, by underrating the importance of practical common-sense methods in the general investigation of nearly all cases. And the old time successful crime investigator should welcome every possible assistance of proven value that science has to offer.

Science is not, by the wildest stretch of the imagination, a substitute for practical methods, as the public has often been led to believe; instead it is just a most valuable acquisition and potent aid which should go hand in hand with plain practical common sense and good judgment in a combined effort to cope with the difficult crime situation that confronts the law-enforcement agencies in every section of the land.”

[1] Reno, Janet, Crime Scene Investigation – A Guide for Law Enforcement. Research Report. U.S. Department of Justice Office of Justice Programs. January 2000, pg. iii.

Attorney General of the United States

As Attorney General Janet Reno stated in Crime Scene Investigation – Guide for Law Enforcement,

“Actions taken at the outset of an investigation at a crime scene can play a pivotal role in the resolution of a case. Careful, thorough investigation is key to ensure that potential physical evidence is not tainted or destroyed or potential witnesses overlooked.

While many agencies have programs in crime scene processing, the level of training and resources available varies from jurisdiction to jurisdiction, as does the opportunity to practice actual investigation.”

Mistakes at the Scene

Few consequences for incompetent investigators

Mistakes are bound to happen Censure does not typically exist. Peer review is akin to the adage

“The fox watching the hen house”

Certification International Association for Identification (IAI) has a

layered crime scene certification program Designed for non-scientists

Needs additional level for more advanced scene investigators and scene scientists In-depth understanding of the scientific concepts, their

limitations AND how and when to apply them

Scene: Where the crime takes placeParticipants - the victim(s), the assailant(s) and the scene(s) -

coincide in time and spacePhysical evidence is found

Edmund Locard - “Every Touch Leaves a Trace.“ An exchange of materialEssential ingredient of forensic science

The Locard Exchange Principle

The Scene

What is Forensic Science?

DefinitionThe application of the techniques of science to

legal matters, both criminal and civil.

Inman & Rudin – without evidence, forensic science could not exist

Forensic vs Forensic Science

Forensic Science (AAFS)

Non-Scientific Disciplines

PathologyJurisprudence

PsychologyDentistry

etc

Scientific Disciplines

ToxicologyAnthropologyEntomologyChemistry

Biologyetc

SceneInvestigations

Forensics

Criminalistics

ForensicsAn umbrella term applied to investigative

professionals who apply standard techniques to answer questions relating to evidence in

crimes.

Crime Scene

Police Department

Medical Examiner

Scene securityEvidence collectionScene documentation

Ascertain medical facts Cause Circumstance Manner

A Typical Scene Investigation

EMSWhat’s Missing???Science!

MLI’s

Mayor

ContaminatesScene

Two Fundamental Principles

of Forensic Science

The Origin of EvidencePrinciple of Divisible Matter

Original Source ofDivisible Matter

Divided MatterAt Scene

Left as Evidence

Divided MatterRemains

With Original Source

The SceneVictimPerpetrator

Fracture Takes Place

Inman & Rudin

Scene

Victim Perpetrator

A Transfer of Anything Among All

Evidence

The Locard Exchange Principle

Criminalistics

Criminalistics Holistic approach

Apply the scientific method

It is both science and a philosophy

Criminalistics is a scientific profession whose members embrace a holistic philosophy encompassing the principles of science, the scientific method, and logic with respect to the analysis of evidence and its relationship to a set of alleged facts

The Forensic DNA Biologist Example

Works in a laboratory

Scientist

Screens the evidence for biological fluid(s)

Conducts scientific tests on samples

Performs DNA analysis

Has limited case information

The resulting DNA profile may be crucial for obtaining a successful prosecution, but the end product of the DNA analysis, generating the

DNA profile, is not the practice of criminalistics

EvidenceWhat it is

How it’s Manifested at the Scene

About Evidence: Read This Carefully

“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothing, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more bear mute witness against him. This is evidence that does not forget.  It is not confused by the excitement of the moment.  It is not absent because human witnesses are, it is factual evidence, physical evidence cannot be wrong, it cannot perjure itself; it cannot be wholly absent, only its interpretation can err.  Only human failure to find it, study and understand it, can diminish its value.'  (Harris vs. Unites States, 331 US 145, 1947)

Dr. Paul Kirk

Two Kinds of Evidence

1. Testimonial: • Given in the form of statements

• Made under oath usually in response to questioning

(In Great Britain, it’s called: “Giving Evidence”)

2. Physical: • Something that is real

• Can take any form

EvidenceWebster - 2006

Something legally submitted to a competent tribunal as a means of ascertaining the truth of any alleged matter of fact under investigation

Something legally submitted to a competent tribunal as a means of ascertaining the truth of any alleged matter of fact under investigation

Anything associated with an incident that may be collected, described, photographed, analyzed or reasoned about and which may be introduced into a legal proceeding in order ascertain the ground truth of an issue.

Working Definition of Evidence

Evidence Dynamics

Evidence DynamicsAn Investigative Concern

Influence on physical evidence Changes Relocates Obscures Obliterates Regardless of Intent

Begins with the crime & ends @ adjudication

Evidence DynamicsInfluences on Evidence

Offender Actions Victim Actions Secondary Transfer Witnesses Weather/climate Decomposition Insect Activity Animal Predation Fire

o Suppression efforts Police EMT's Scene Investigators Forensic Scientists/forensic entomologist/Criminalists Medical Examiners/coroners

Five Manifestations of Evidence

Predictable Effects Changes that occur with rhythm or regularity

Forensic entomologyForensic medicine

Unpredictable Effects Unexpected or Random – can be misinterpreted

Bystanders/witnessesEMTPolice entry to scene

Manifestation of Evidence

Transitory Effects Fleeting evidence Requires diligence by

investigator – first officer – to observe & note

Provides a factual reference Odors Melting Ice in glass Tire signature on roadway

Relational Detail Investigator’s ability to

correlate evidence @ the scene Void patterns Cluster of shell

casings Muzzle-target

distance estimation

Manifestation of EvidenceFunctional Detail

Does it work?The gun at the sceneThe locks on the doorsClock that stopped

Logic at the SceneA Case Example

Case Facts: Secondary Response

Homicide Saw struggle Saw someone leaning across seat from passenger side

Gunshot wound to right side of head

Weapon missing

CSI already processed car Passenger door removed

Other considerations Brother recently committed suicide Had been drinking heavily

Deceased SittingIn Driver’s Seat

Source ofSecondary Spatter

Secondary SpatterBackspatter

Critical Bloodstain

Blood + associated tissue stain

Created when door was closed

Similar stainSpans door gap