Intro to Forensics
I. Introduction to Crime and Forensic Evidence
Crime occurs in various locations (workplace, schools, homes, streets, Internet) and times, in rural, suburban, and urban environments.
Weapons like handguns, knives, or blunt objects may be used; perpetrators might be under the influence of alcohol or drugs.
Property damage or theft (burglary, theft, motor vehicle theft) are common, as are identity theft and cybercrime.
Crime scenes yield rich information, including blood, saliva, skin cells, hair, fingerprints, footprints, clothing fibers, digital/photographic images, audio data, handwriting, and evidence of arson, gunshots, or unlawful entry.
Crime scene investigators collect, preserve (in tamper-evident packaging), label, and send evidence to appropriate agencies, usually crime laboratories.
II. Medicolegal Investigation
If a death is sudden, unexpected, or results from violence, a medicolegal investigator (e.g., coroner, medical examiner, forensic pathologist) determines whether a homicide, suicide, or accident occurred and certifies the cause and manner of death.
III. Core Activities of Forensic Science
Forensic science "attempts to uncover the actions or happenings of an event" through:
In forensic science, the core activities for uncovering the actions or happenings of an event involve four key processes:
Identification (categorization):
This process involves determining the physical or chemical identity of a substance or object. It categorizes the evidence into a known group from a larger class of items. For example, identifying a white powder as a specific drug or a blood sample as human blood.
Individualization:
This refers to the process of linking a piece of evidence to a single, unique source, proving that it originated from that specific source to the exclusion of all other possible sources. Examples include matching a fingerprint to a specific person or a bullet casing to a specific firearm.
Association:
Association establishes a connection or relationship between two or more items of evidence, between evidence and a person, or between evidence and a crime scene. It suggests that these entities were related in some way, such as a fiber from a suspect's jacket found on a victim's clothing.
Reconstruction:
Reconstruction is the process of determining the sequence of events that occurred at a crime scene. It involves piecing together the evidence to understand the order and nature of actions that took place. This could include analyzing blood spatter patterns to understand the dynamics of an assault or tire marks to reconstruct a vehicle's movement.
Evidence is also analyzed with the purpose of excluding individuals or sources, which is equally critical in forensic investigations to narrow down potential suspects or origins.
Individualization
Association
Reconstruction
Evidence is also analyzed to exclude individuals or sources.
IV. Forensic Service Providers
Not all forensic services are performed in traditional crime laboratories by trained forensic scientists; some tests may be conducted by sworn law enforcement officers with no scientific training beyond experience.
In smaller jurisdictions, local police or sheriff's departments might conduct analyses like latent print examinations and footwear comparisons.
Crime laboratories can be publicly or privately operated in the United States.
Private laboratories typically do not visit crime scenes or serve as the first recipient of physical evidence.
Public laboratories are organized at city, county, state, or federal levels.
According to a 2005 census by the Bureau of Justice Statistics (BJS):
389 publicly funded forensic crime laboratories operated in the U.S.
These included 210 state or regional, 84 county, 62 municipal, and 33 federal laboratories.
They received evidence from nearly 2.7 million criminal cases in 2005.
Staff have a wide range of training, from Ph.D. scientists to on-the-job trained technicians.
A traditional crime laboratory typically analyzes evidence in disciplines such as controlled substances, trace, biology (including DNA), toxicology, latent prints, questioned documents, firearms/toolmarks, or crime scene investigation.
Increasingly, laboratories specialize in single areas, like DNA or digital evidence.
V. Pressures on the Forensic Science System
A. Case Backlog
A typical publicly funded crime laboratory in 2005 ended the year with a backlog of about 401 requests, received 4,328 new requests, and completed 3,980. Roughly half of all requests were for controlled substances.
The average backlog increased since 2002, with nearly 20 percent of requests backlogged.
The Department of Justice (DOJ) defines a case as backlogged if it remains in the laboratory 30 days or more without a report or analysis.
Federal, state, and local laboratories reported a combined backlog of 435,879 requests for forensic analysis in 2005.
A typical lab performing DNA testing in 2005 started with 86 requests, received 337 new ones, completed 265, and finished with 152 backlogged requests.
Backlogs are exacerbated by increased requests for quick results and additional work prior to trial, as well as rising requests for DNA testing from nonviolent crime scenes.
Proposition 69 in California, which requires DNA samples from all convicted felons, led to 235,000 backlogged cases by the end of 2005.
Consequences include prolonged incarceration for innocent persons, delayed investigations, potential release of guilty suspects, and issues with speedy trials; backlogs can also discourage evidence submission or lead labs to restrict submissions.
B. Ascendancy of DNA Analysis and a New Standard
In the 1980s, DNA technologies offered new opportunities for identification.
Early concerns regarding scientific validity (correctly identifying matches/nonmatches) and reliability (reproducible results).
A 1990 report by the Office of Technology Assessment affirmed DNA tests as reliable and valid, but noted the need for strict standards and quality control.
The FBI established DNA analysis guidelines (1990) and created the Combined DNA Index System (CODIS, 1994) for electronic DNA profile exchange.
National Research Council (NRC) reports (1992, 1996) emphasized proficiency testing via blind trials, addressed contamination, degradation, and statistical issues, and recommended new statistical calculations and improvements in laboratory performance and accountability.
Tremendous growth in DNA evidence use: over 175 public and approximately 30 private labs perform hundreds of thousands of DNA analyses annually in the U.S.
President George W. Bush's 2003 "President's DNA Initiative" was a 5-year, 1 billion program to maximize DNA technology's potential.
DNA analysis has set a higher standard for other forensic science methodologies due to its well-defined precision and accuracy, offering a higher degree of reliability and relevance.
Limitation: DNA evidence comprises only about 10 percent of casework and its relevance depends heavily on the specific context of the criminal event.
C. Questionable or Questioned Science
Increased DNA analysis has led to reevaluation of older cases, revealing a disturbing number of wrongful convictions (e.g., 223 post-conviction DNA exonerations since 1989 as of November 2008) and serious limitations in some traditional forensic approaches.
Many forensic tests (e.g., toolmarks, bite marks) have not been subjected to stringent scientific scrutiny; they were often developed in crime laboratories without prioritizing research into their limitations and foundations.
While practitioners have worked to improve methods, the precise error rates of these tests are largely unknown, and comparisons with DNA testing have revealed erroneous results.
Fingerprint analysis, long considered an exact means of identification, has recently been questioned regarding its scientific foundation and reliability, particularly in correlating imperfect latent prints with known prints (e.g., Judge Susan M. Souder's 2007 ruling).
The goal of "individualization" in methods like shoe/tire impressions, dermal ridge prints, toolmarks, firearms, and handwriting implies that evidence originated from a unique source to the exclusion of all others. This requires objective measurements, data on population frequency, testing of attribute independence, and public research, which has often been lacking.
The Detroit Police crime laboratory was shut down in 2008 due to a 10 percent error rate in ballistic evidence.
The forensic science community lacks sufficient funding for independent research and enforceable standards for data interpretation.
D. Errors and Fraud
The integrity of crime laboratories has increasingly been questioned due to highly publicized cases of lax standards, questionable or fraudulent evidence, and insufficient quality control.
Notorious examples include Fred Zain (West Virginia State Police laboratory), who repeatedly falsified evidence, leading to doubts about over 100 convictions, and scandals involving the Houston Crime Laboratory.
VI. What is Forensic Science?
A. Categorization of Disciplines (National Institute of Justice)
General toxicology
Firearms/toolmarks
Questioned documents
Trace evidence
Controlled substances
Biological/serology screening (including DNA analysis)
Fire debris/arson analysis
Impression evidence
Blood pattern analysis
Crime scene investigation
Medicolegal death investigation
Digital evidence
B. Variability and Nature of Disciplines
Forensic medicine (e.g., forensic pathology) is considered a medical subspecialty.
Forensic science encompasses a broad range of disciplines with wide variability in techniques, methodologies, reliability, error rates, research, general acceptability, and published material.
Some disciplines are laboratory-based (e.g., nuclear/mitochondrial DNA analysis, toxicology, drug analysis); others rely on expert interpretation of observed patterns (e.g., fingerprints, writing samples, toolmarks, bite marks).
Activities are conducted by individuals trained as scientists (chemists, biologists), in law enforcement (crime scene investigators, blood spatter analysts), medicine (forensic pathologists), or laboratory methods (technologists).
Many processes are empirical applications of science, not always based on a body of knowledge that recognizes the underlying limitations of scientific principles and methodologies.
It is crucial to improve, systematize, and monitor these activities.
The term "forensic science" is used broadly, acknowledging that some activities may lack a well-developed research base, scientific knowledge, or a scientific culture.