Case 1 -
Forensic Sciences: Injury Causation: A Primer
Glenn N. Wagner
Chief Medical Examiner, County of San Diego
San Diego, CA
The CSI TV series has done much to promote the interactions of the crime laboratory with the forensic
pathology practiced in the medical examiner's or coroner's office. Both institutions utilize multiple
disciplines in forensic science to pursue their investigations and collectively provide a comprehensive
analysis of the incident and its players. This presentation focused on the characteristics of the San
Diego experience will address the issues of victim identification, evaluation of the cause of death, and
investigating the circumstances of death leading to an opinion as to manner of death-natural, accident,
suicide, homicide or undetermined. The character of the case defines its investigation. In some cases,
the focus is on public health; in others, public safety.
Forensic Sciences: Injury Causation: A Primer
In the forensic sciences there are a number of questions asked in any medicolegal inquiry: Who, What,
Where, When, How, By Whom, and Why. For the medical examiner/coroner the focus is on the requirements
of the death certificate: identification, cause of death, and opinion as to manner of death. The latter
is determined by the circumstances surrounding the injury and death. The medicolegal investigation is a
series of phased inquiries beginning with incident reporting and fact acquisition, followed by analysis
and interpretation, followed by conclusions, and if required recommendations. There often are several
boards of inquiry on a particular incident depending on the nature of that incident: medical
examiner/coroners inquiry/inquest, criminal investigation, safety investigation, etc each with different
goals and objectives, rules of evidence, and SOPs.
At the same time, there are concurrent autopsies: victims, vehicle (if appropriate), scene, physical
evidence, and mission. Reconstruction of the events and the factors leading up to those events is
dependent on the accuracy and relevance of those "independent" linked inquiries. Documentation of
findings with sketches, diagrams, film, radiographs, and reports is critical. Linking those reports, or
even knowing of their existence, is problematic, particularly if there are different jurisdictions. The
medical inquiry, usually by the medical examiner/coroner, is structured based on the information
available from the scene through personal attendance and/or investigators, police and EMS reports, if
available, and information from witnesses and or family members. The latter is usually obtained during
notification of next of kin or is volunteered or solicited during the investigation.
The cause of death, a primary concern is related to injury causation. Injury causation has been
approached by investigators in a number of modes: classification of traumatic or environmental injuries
by cause, disease states by etiology, and human factors by behavior, disposition and opportunity.
Examples of these follow:
Classification of Trauma by Cause
- gun shot wounds
- sharp force injuries
- blast injuries
- radiation injuries
- blunt force injuries
- thermal injuries
- drowning injuries
The vast majority of these traumatic injuries are from an applied force which has (1)
magnitude-weight, velocity, (2) direction, (3) frequency, and (4) duration. Characterization of these
qualities often assists in identifying the instrument or trauma biomechanics.
Agents of injury are important in the analysis of trauma because the source of the force energy
affects both the degree and distribution of that injury. The body's reaction to injury is what is
observed by the clinician and pathologist, not the actual kinetic energy causing that presentation. It
has come and gone.
Common Surface Injuries
|Abrasion ||an injury to the surface of skin |
|graze|| ||rough surface|
|imprint|| ||localized pressure|
|scratch|| ||a pointed object|
|Avulsion ||tearing away of a part or tissue ||movement of a heavy object-a tire|
|Blister ||fluid collection under the skin ||heat, skin diseases, infections, drugs, poisons, putrefaction|
|Bruise ||hemorrhage into subcutaneous ||blunt force, blood tissues diseases|
|Contusion ||injury to tissue without disruption ||blunt force|
|Cut ||an incised wound, longer than deep ||sharp object|
|Laceration ||crushing or tearing injury ||trauma|
|Split ||longitudinal laceration of skin ||compression between bone and hard object or surface|
|Stab ||penetrating wound, deeper than wide ||pointed object|
Classification of Disease by Etiology
These are conditions that through examination and laboratory studies can be identified, diagnosed and
usually understood as to progression based on the pathophysiology. They are generally approached by
Aside from being the medical reason for an injury or response to an injury, these categories are
usually evaluated relative to cause of death as incidental, contributory or proximal. In general, sudden
death can only occur in three body systems: Nervous, Respiratory or Cardiovascular Systems.
Understanding the pathophysiology is critical to understanding the medical condition and its stage or
progression. Structure directs function and function influences structure.
- Cardiac-acute myocardial infarct (AMI), coronary artery disease (CAD), atherosclerotic cardiovascular
diseasee (ASCVD), arrhythmias (altered heart beats), myocarditis (infection of the heart muscles),
cardiomyopathy, endocarditis or valvulopathy.
- Respiratory-pneumonia, pulmonary embolus, airway obstruction, poisoning, compression
- Neurological-CVA (stroke), encephalitis, meningitis, subdural/subarachnoid or epidural hemorrhages,
paralysis, dementia, tumor
- Hepatic-cirrhosis, acute necrosis, hepatitis, tumor, other infiltrative process
- Renal-renal failure, sepsis, tumor, other infiltrative process, autoimmune
- Gastrointestinal-hemorrhage, obstruction, infection and peritonitis, tumor
- Lymphoreticular-immunocompromised, anemia, cytopenic, tumor, inflammation
- Endocrine-endocrinopathies-failure of pituitary, thyroid, parathyroids, adrenal glands, pancreas, sex
- Musculoskeletal-tumors, infections, congenital defects, metabolic, inflammatory
- Cutaneous-infections, inflammatory, tumors, burns
The strategic planning for litigation in cases involving impact trauma depends on the state of art in
quantitative biophysical/biomechanical experiments and analysis of the minimum value of the injury
causing force, its direction, and its velocity. The analysis follows Newton's principles of physics on
the three laws of motion. First Law: If a force is exerted on a movable or moving object, it will
change its state of motion. Second Law: If a force is exerted on an object, the object will move in the
direction of applied force and, the more massive the object, the more force it takes to move it (F=ma).
Third Law: If you exert a force on an object, the object exerts an equal and opposite force on you.
Human Factors-Behavior, Disposition, Opportunity
- education and training
- speech and communication
- epidemiology-trends and patterns
These categories are a mix of subjective and objective evaluations that color what is found and how it
is interpreted. Intent may be assessed by actions or evidence of a preconceived plan. Cognition may be
assessed by the victim's or perpetrator's understanding of the consequences of an action or reaction.
Capability evaluations are based on the individual's training and education, possibly level of
development. Standardized testing may be appropriate to determine level of development, understanding
and motor skills. Opportunity, based on geography, time, anthropometrics, intent can be used for modus
Human factors analysis should be an important aspect of a number of medicolegal investigations.
Studies have shown that in the majority of motor vehicle mishaps-automobiles, motorcycles, trucks,
trains, buses and aircraft, human factors contribute as much as 70-80% of the risk factors. In such
transportation mishaps particularly, the issue of survivability is raised. Was this a survivable
accident? For the forensic scientist, pathologist, investigator, engineer, or lawyer, this can often be
addressed by assessing three primary parameters: crash forces-both decelerative and impact, occupiable
space, and post crash environment-especially fire and water. Pathologists, surgeons, and engineers are
always looking to refine the biomarkers of trauma relative to magnitude and direction. What does it take
to break this from this attitude (position, direction), for this duration (time)? Are the parameters
measurable relative to intent? Are parameters experimentally determined in mathematical models, animal
or human cadaver studies valid and applicable to living victims? There is almost always a safety
component. Was the training and skill of the operator adequate? Was there a mechanical malfunction?
Were there appropriate restraints? Were they used? Is there evidence of decreased capability based on
medical conditions or toxicology studies? Did fatigue, dehydration, diabetes, exertion, hypothermia or
hyperthermia play a role?
In child abuse cases, the first indicator is usually an infant or child presenting to a clinic,
hospital, school, social workers, law enforcement or morgue whose physical findings are not in keeping
with a solicited history. The majority of these cases involves either suspected physical or sexual
abuse, neglect or abandonment rather than mental abuse. There are a number of controversial areas in
these cases such as the shaken baby syndrome, SIDS, infants or children with congenital or metabolic
defects, eg. osteogenesis imperfecta, and biochemical abnormalities. Munchausen by Proxy is currently
receiving a considerable amount of interest and is often quite difficult to prove in the absence of
documented activities on the part of the parent or caretaker. Often these investigations are
precipitated by a repeated event within a family that receives more scrutiny for one reason or another.
In recent times, a similar effort has been directed at Elder Abuse, in part driven by an increasingly
aged population and in part a different cultural perspective on "acceptable" conditions. In both cases,
there are reasonably well understood risk factors and identifiable triggers. Both areas are often
addressed by a multidisciplinary and usually multifactorial investigative effort recognized as a public
health and safety concern.
This author believes that both these areas of domestic violence require a similar or same level of
medical documentation to include extensive imaging and behavioral/development assessments as well as
medical and laboratory examinations.
Forensic pathology usually involves the practice of autopsy pathology, microscopy and toxicology.
There is significant reliance on other disciplines for additional data-forensic odontology (dentistry),
forensic anthropology, forensic serology and molecular diagnostics (DNA profiling), criminalistics and
forensic psychology and psychiatry. The "stitching" of these disciplines does not necessarily happen
exclusively with or through the medical examiner or coroner. It often comes about either from law
enforcement, the DA or defense teams particularly if there are unresolved temporal (when or where) or
behavioral (why, how) issues.
Lethality: Not all fatal injuries are immediately fatal. There is usually a survival or
agonal period during which a victim and/or perpetrator can continue a course of action or initiate a
course of action that might influence what is interpreted from the body, the scene evaluation and
physical evidence. The time interval between injury and death continues to be a topic of discussion and
laboratory inquiry. Laboratory evaluations are based on more precise understanding of the underlying
Defense Wounds: A defense wound is a term often applied to certain findings in trauma victims
where the injury or injuries are attributed to defensive posturing on the part of the victim during the
assault. These injuries are usually on the victim but can also be on the perpetrator. Fingernail
scratches, bitemarks, punching or kicking injuries are examples of such injuries where wound character
and location are both important. The term is most frequently is used in sharp force cases where elements
of incising or slicing and stabbing are being sorted. It may equally be applied to certain gunshot
wounds and patterned blunt force injuries.
Time of Death: The estimation of the time of death in unwitnessed events ranges from minutes
to seasons to years depending on what remains and in what condition. The longer the interval, the
greater the variance in most cases. Bodies buried in soil fare better than those in water or remaining
on the surface. In recent deaths, rigor mortis, livor mortis, calor mortis are the measured parameters
most frequently used. Body temperature is still considered the most useful single indicator of the time
of death during the first 15 hours. With decomposition which is a mix of putrefaction and autolysis
there are substantial changes to the body including gas distention, discoloration, liquefaction, and
disintegration. Occasionally the remains are more preserved than expected because of environmental
conditions causing mummification or formation of adipocere. Environmental clues are frequently used to
assist in PMI estimation including entomology, plant pathology, soil stratification, personal effects and
Postmortem changes are of value to the pathologist because they:
- confirm the fact of death
- provide a rough indication of the time of death
- may indicate that the body has been moved after death
- may reflect the cause of death
- may be mistaken for pre-mortem lesions
- rapidly destroy signs of soft tissue injury and many features upon which identity is
In the ideal world fact and truth are synonymous. In reality, especially in the legal system, they
are not necessarily the same. A fact is a circumstance, event or conclusion presumably based on the
truth. It is the duty of the jury to determine the facts. Admissibility is a key determinant of facts
offered for consideration and judgement. Key issues are fidelity, accuracy, and sincerity in searching
for the facts and on faithfulness, exactness and probity in reporting the results of an investigation.
Evidence is testimony, writings, material objects, and other things offered to prove the existence or
nonexistence of a fact.
Generally, there are three phases to a medicolegal investigation; (1) Why did the person die? (2) By
what means and in what manner did death take place? And (3) Who was responsible? It is also generally
accepted that three "bridges" are burnt behind the investigator: (1) movement of the body, (2) embalming
of the body, and (3) disposition of the body-burial or cremation. Once the body is moved it cannot be
exactly restored. This fact emphasizes the need for accurate documentation-identification, measurements,
and photographs. Embalming fundamentally changes the chemical composition of the body and alters
toxicology clues. At the same time it can preserve and enhance certain wound characteristics.
Disposition of the remains is often today accomplished through cremation destroying any physical evidence
that might still be present and interpretable.
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