Forensic Biology Overview

Forensic Biology Overview

Definition of Forensic Science

• Forensic Science encompasses the application of biological and chemical sciences to resolve problems relevant to the administration of justice.
• It is a scientific discipline serving the law.

Purpose of Forensic Science

• The core goal of forensic science is to help establish facts that are in dispute during legal inquiries.
• Relevant questions typically include:
  • What
  • Why
  • When
  • How
  • Where
  • Who

Key Principle

• "Every contact leaves a trace" - Locard.

Locard's Exchange Principle

• This principle posits that any interaction between an individual and an environment creates a physical trace.
• Quote by Locard:
  • "Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as silent witness against him. Not even his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the semen he deposits or collects—all of these 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.”

Branches of Forensic Science

• Biological Sciences:
  • Includes DNA analysis and serology.
  • Engages with trace evidence such as hairs and fibers.
• General Chemistry:
  • Essential for various forensic applications.
• Physical Examinations:
  • Involves analyzing tool marks, tire tracks, and shoe prints.
• Arson and Explosives Investigation:
  • Examines evidence related to fire-related crimes.
• Firearms:
  • Analysis of weaponry used in crimes.
• Documents and Counterfeits:
  • Studies authenticity and forgery of documents.
• Toxicology:
  • Examines controlled substances and toxic agents.
• Digital Evidence:
  • Information that is stored or transmitted in a binary format.
• Crime Scene Investigation:
  • Integrates various disciplines to analyze evidence at crime scenes.
• Latent Print Examination:
  • Deals with the identification of fingerprints.

Specialized Fields of Forensics

• Forensic Pathology:
  • Conducts autopsies to determine causes of death, time of death, and manner of death (natural, homicide, suicide, undetermined).
• Forensic Anthropology:
  • Involves the identification and examination of human skeletal remains, revealing an individual’s origin, sex, approximate age, and injuries.
• Forensic Entomology:
  • Studies insects in relation to a criminal investigation to estimate time of death based on stages of insect development.
• Forensic Odontology:
  • Focuses on the identification of victims through dental characteristics and bite mark analysis.

Serology and Forensic Biology

• Serology:
  • The study of serum composition and properties relevant to blood identification in criminal cases.
  • Also known as: forensic biology, forensic biochemistry, forensic molecular genetics, bio-molecular forensics, forensic genomics.
• Focus Areas:
  • Identification of bodily fluids (e.g., blood, saliva, semen).
  • Blood drop dynamics and individualization through biochemical genetics/molecular biology/genomics.

Types of Crimes Addressed by Forensic Biology

• Crimes Against Individuals:
  • Homicide
  • Assault
  • Rape/Sexual Assault
  • Criminal Paternity
• Crimes Against Property:
  • Burglary
  • Motor Vehicle Accidents
  • Missing Persons
  • Mass Disasters

Case Illustrations

• The “Direct to DNA argument”:
  • Suggests that finding a suspect’s DNA can be used as definitive proof of involvement.
  • Notably, tests primarily identify DNA from blood and semen only.

Practical Cases in Forensic Biology

• Case Example: Sexual assault involving an object recovered from the suspect with the victim’s DNA.
• Defense Argument:
  • The defense may claim that the victim's DNA was present due to prior casual contact, not assault.
  • The determination of vaginal secretions would be significant, indicating a sexual encounter.
• Additional Case Example: A businessman found strangled with a necktie, DNA recovered linking to a business partner with a motive.

Collection and Preservation of Biological Evidence

• Evidence collection should prioritize the likelihood of revealing meaningful information.
• Assess the relevance of each evidence item at crime scenes.
• Ensure proper collection techniques to avoid contamination and maintain integrity:
  • Evidence should be preserved in breathable containers (e.g., paper bags).
  • Evidence items should be kept dry and stored separately to prevent cross-contamination.
• Collection steps:
  1. Collect the entire item when feasible.
  2. Cut stains from larger items (e.g., cloth).
  3. Transfer stains minimally using distilled or deionized water.
  4. Scrape or chip stains from non-porous surfaces.
  5. Collect control samples in the same manner as the stain.

Environmental Factors Impacting Evidence

• Heat: Rates of reaction double for every 10°C increase, potentially damaging DNA.
• Light: Can cause chemical cross-links and DNA damage.
• Humidity: Promotes microbial growth and hydrolytic degradation of evidence.

Recording and Analyzing Evidence

• Importance of accurate records during evidence analysis:
  • Document tests, conditions, standards, and controls.
  • Maintain logbooks and preserve photographs.
• Chain of custody must be maintained, detailing who delivered/received evidence, identifying information, and significant stains.

Conclusion

• Forensic biology plays a critical role in the justice system by providing scientific evidence through various specialized fields of study. Proper handling, collection, and analysis of biological evidence are paramount to ensuring justice and the integrity of the forensic process.