Section 3.3: Blood and Biological Evidence

Fundamentals of Criminal Investigation by Adam J. McKee

Biological evidence encompasses a wide range of biological materials found at crime scenes, including hair, tissue, bones, teeth, blood, semen, and other bodily fluids, as well as items containing these materials. The meticulous handling, preservation, and analysis of biological evidence are cornerstone practices in forensic science, vital for ensuring the integrity of the criminal justice process.

Role of Biological Evidence

  • Linking or Excluding Individuals: Biological evidence plays a crucial role in associating individuals with a crime scene or excluding them from suspicion. Its analysis can provide definitive conclusions about a person’s involvement in a crime, making it a powerful tool in both investigation and prosecution.
  • Influence on Judicial Outcomes: The presentation of biological evidence in court significantly impacts the decision-making process, aiding judges and jurors in determining the guilt or innocence of defendants. Its clarity, reliability, and relevance are paramount for fair and just verdicts.

Preservation and Handling

  • Proper Preservation: To maintain the evidential value of biological materials, it’s essential that they are preserved in conditions that prevent contamination, degradation, or premature destruction. This ensures that samples can be analyzed accurately when needed for court proceedings or forensic testing.
  • Efficient Storage and Tracking: Biological evidence must be stored in an appropriate facility, where it’s properly labeled and easy to retrieve. This organization is crucial for evidence custodians and others who might need to access the evidence for analysis or court presentations.

Responsibilities of Stakeholders

  • Criminal Justice Stakeholders: Law enforcement officers, forensic analysts, lawyers, and fact-finders all rely on biological evidence. It is essential that each party understands the importance of the evidence being properly preserved, processed, and stored to uphold the standards of justice.
  • Evidence Handlers: Those directly involved in the handling of biological evidence, including evidence custodians, must ensure that it is packaged and labeled clearly. This not only facilitates efficient retrieval but also safeguards against potential cross-contamination or loss.

Best Practices for Handling Biological Evidence

To ensure the integrity of biological evidence, all individuals involved in its handling must adhere to stringent procedures for its collection, packaging, labeling, storage, and analysis. These best practices are essential for preserving the evidence’s condition and probative value, ultimately supporting the pursuit of justice.

🔍 Reflect

How does the meticulous management of biological evidence impact the overall integrity of criminal investigations and the fairness of judicial proceedings?

Ensuring Safety in Handling Biological Evidence

Handling biological evidence carries inherent risks, particularly due to the potential presence of bloodborne pathogens that can transmit diseases. It is imperative that all individuals who come into contact with biological evidence adopt stringent safety measures to mitigate these risks. This section outlines key safety protocols and the importance of personal protective equipment (PPE) in maintaining a secure environment when dealing with biological materials.

Recognizing the Hazards

  • Potential for Disease Transmission: Bodily fluids, including blood, semen, and saliva, can harbor viruses and bacteria capable of causing illness. Pathogens such as HIV, hepatitis B, and hepatitis C are of particular concern due to their prevalence and the severity of diseases they can cause.

Personal Protective Equipment (PPE)

  • Essential Gear: To protect against exposure to hazardous materials, wearing appropriate PPE is crucial. This includes gloves, face shields or goggles, masks, and protective clothing. Each piece of equipment serves to create a barrier between the individual and the biological evidence, significantly reducing the risk of transmission.
  • Proper Use and Disposal: Beyond simply wearing PPE, it is important to use it correctly and dispose of it safely after use. This includes following protocols for putting on and removing gear to avoid contamination, as well as disposing of used PPE in designated biohazard containers.

Handling and Transportation Protocols

  • Safe Handling Practices: When collecting, packaging, and transporting biological evidence, it’s essential to use techniques that minimize direct contact with the materials. Tools such as tweezers, forceps, and swabs should be used whenever possible to handle evidence without direct skin contact.
  • Secure Transportation: Biological evidence should be transported in leak-proof containers clearly labeled as biohazardous. This not only protects those handling the evidence but also ensures the integrity of the samples for testing.

Training and Awareness

  • Education on Risks and Protocols: Regular training for all individuals who may encounter biological evidence is necessary to ensure they are aware of the potential risks and know how to protect themselves effectively. This training should cover the use of PPE, safe handling practices, and emergency procedures in case of exposure.
  • Creating a Culture of Safety: Fostering an environment where safety is prioritized and protocols are rigorously followed is essential in minimizing the risks associated with handling biological evidence. This culture of safety helps protect individuals from potential harm and ensures that evidence is handled in a manner that preserves its integrity for forensic analysis.

By adhering to these safety recommendations, individuals handling biological evidence can significantly reduce their risk of exposure to harmful pathogens, ensuring their own safety as well as maintaining the integrity of the evidence for forensic purposes.


Consider the implications of inadequate safety protocols in the handling of biological evidence. How might this affect the individuals involved and the overall integrity of the forensic analysis?

Understanding Biological Evidence

The landscape of biological evidence in forensic investigations is vast and nuanced, shaped significantly by state laws and the advancements in DNA technology. With the introduction of touch DNA analysis, the range of items considered as potential carriers of biological evidence has expanded dramatically, underscoring the need for clear guidelines on evidence retention.

The Spectrum of Biological Evidence

  • Diverse Sources: According to the National Institute of Justice, biological evidence can originate from a wide array of items, from the more traditional sources like bloodstains and hair follicles to modern advancements enabling the collection of touch DNA from virtually any object a person has contacted. This diversity highlights the potential each item holds for uncovering crucial forensic information.
  • Touch DNA: This form of DNA evidence, derived from skin cells left behind when a person touches an object, has opened new avenues for forensic analysis. Touch DNA can be collected from a myriad of surfaces, significantly broadening the scope of what can be considered biological evidence.

Challenges of Evidence Retention

  • Legal Variability: Definitions of what constitutes biological evidence can vary from one jurisdiction to another, complicating the standards for evidence retention across different regions. This variability necessitates a careful review of local laws and guidelines when determining how to manage and store biological evidence.
  • Storage Limitations: The imperative to retain all physical evidence that might contain DNA poses significant logistical challenges, particularly in terms of storage capacity. Law enforcement agencies are tasked with finding a balance between the demands of justice—which favors broad evidence retention—and the practical limitations of physical storage space.

Establishing Retention Thresholds

  • Balancing Justice and Practicality: To navigate the complexities of biological evidence retention, law enforcement agencies must establish minimum thresholds for what is kept in storage. These thresholds should be designed to preserve evidence with the highest potential relevance to criminal cases while considering the finite nature of storage resources.
  • Adapting to Technological Advances: As DNA analysis technology continues to evolve, the criteria for evidence retention may need to be revisited regularly. Keeping pace with technological advancements ensures that retention policies remain effective and aligned with the capabilities of forensic science.

The management of biological evidence, with its ever-expanding scope due to technological advances like touch DNA, presents both opportunities and challenges for the criminal justice system. Developing clear, adaptable guidelines for evidence retention is crucial for ensuring that valuable forensic information is preserved without overwhelming storage capacities, thereby supporting the overarching goals of justice and public safety.

Reflect: 🔍 How do advancements in DNA analysis technology, such as the ability to collect touch DNA, impact the strategies for managing and retaining biological evidence?

Managing Bulky Items in Forensic Evidence

In criminal investigations, the integrity and accessibility of forensic evidence are paramount, especially when preparing for trial and post-conviction reviews. However, the logistical challenges of storing and tracking large or bulky items, which may carry crucial biological evidence, necessitate strategic decision-making to balance space constraints with the needs of justice.

Challenges with Bulky Evidence

  • Space Constraints: The physical storage of large items, such as vehicles, large pieces of furniture, or sections of carpeting, poses significant challenges due to the substantial space they require.
  • Preservation of Biological Material: Often, the value in bulky items lies in the biological material they bear. The size of the item itself, while potentially cumbersome, is less critical than the evidence it hosts.

Strategic Approaches to Bulky Evidence

  • Sample Retention: In many cases, retaining samples extracted from bulky items may suffice, assuming these samples contain the biological evidence pertinent to the case. This approach allows for the preservation of crucial forensic material without the need to store the entire object.
  • Documentation: Rigorous documentation, including detailed photographs, sketches, and comprehensive case files, can ensure the context and relevance of the samples are well understood. This documentation is vital for establishing the provenance and significance of the samples in lieu of the original bulky item.

Considerations for Bulky Items

  • Selective Retention: Decisions on what to retain should consider the item’s evidentiary value, the feasibility of storage, and the likelihood of future testing needs. For example, while a vehicle involved in a hit-and-run might be critical, a large piece of furniture with a minor role in the case might not.
  • Digital and Photographic Archives: Modern technology offers robust solutions for preserving the evidential context of bulky items. High-quality digital photographs and 3D modeling can provide an accurate representation of how biological evidence was situated on the item, facilitating future analysis without requiring physical retention of the object.

Implementing Effective Policies

Law enforcement agencies and forensic storage facilities must develop clear, practical policies for managing bulky evidence. These policies should prioritize the retention of biologically significant samples and support detailed documentation to ensure evidence remains accessible and interpretable for as long as necessary, all while managing the practical limitations of physical storage space.

By adopting strategic approaches to the storage and documentation of bulky items, investigative and forensic entities can maintain the integrity of crucial evidence while addressing logistical challenges, ensuring that justice is both served and sustainable.

🔍 Reflect

How might advances in technology further aid in the management of bulky forensic evidence, and what are the potential implications for the justice system?

Case Status and Its Impact on Evidence Retention

In criminal justice, a case’s status plays a critical role in determining how long biological evidence should be retained. This evidence, which can include anything from hair and blood to other bodily fluids, is often pivotal in solving crimes and securing convictions. Here’s a breakdown of the four general categories of case status and their implications for evidence retention.

Open Cases

  • Definition: Cases where a suspect has not been identified or charged, but the investigation continues.
  • Retention Protocol: Biological evidence in open cases should be preserved indefinitely for homicides and at least until the statute of limitations expires for all other offenses. This ensures that crucial evidence remains available as long as there is potential for case advancement.

Charges Filed

  • Definition: Cases where a suspect has been charged, and court proceedings are active or impending.
  • Retention Protocol: All evidence in prosecuted cases must be retained to support ongoing or future analysis and court proceedings. A communication link between investigators, prosecutors, and evidence custodians is vital for managing evidence based on the case status.

Adjudicated Cases

  • Definition: Cases with a final judgment, such as a conviction, dismissal, or acquittal.
  • Retention Protocol: The retention of biological evidence varies by crime category but generally should be preserved through the period of incarceration for serious offenses (e.g., homicides, sexual assaults). For less severe Group A and B offenses, evidence may be disposed of post-adjudication, following state retention statutes and with appropriate authorizations.

Unfounded Cases

  • Definition: Cases deemed unfounded, refused, denied, or not pursued further, including instances where charges are not filed or investigations are exceptionally cleared.
  • Retention Protocol: Evidence can be disposed of once disposition approval is received, except where law explicitly requires retention. This category accommodates scenarios where legal action is not pursued, streamlining evidence management without compromising legal obligations.

Implications for Evidence Management

Understanding and appropriately applying these case status categories are essential for managing biological evidence effectively. It ensures that evidence is available when needed for legal proceedings while also addressing storage limitations and respecting statutes of limitations. By maintaining clear protocols based on case status, law enforcement agencies can uphold the integrity of the evidence and, by extension, the criminal justice process.

The Importance of Clear Communication

Establishing and maintaining clear communication channels among all stakeholders involved in a case—from law enforcement officers to prosecutors and evidence custodians—is crucial. This coordination ensures that the status of evidence is accurately tracked and managed throughout the judicial process, facilitating timely decisions regarding evidence retention or disposal.

🔍 Reflect

How do the challenges of evidence retention highlight the importance of collaboration and communication among criminal justice stakeholders?

Packaging and Storage of Biological Evidence

The meticulous packaging and storage of biological evidence are critical to preserving its integrity for forensic analysis. Recent requests for evidence production have highlighted deficiencies in these areas, underscoring the need for more rigorous procedures to prevent contamination and degradation. Here’s a comprehensive guide on optimizing the preservation of biological evidence.

Overcoming Storage Challenges

  • Facility Limitations: The capacity and management of storage facilities often impede the optimal preservation of evidence. Addressing these limitations requires strategic planning and resource allocation.
  • Packaging Materials: The availability of suitable packaging materials is essential. Jurisdictions must ensure that evidence handlers have access to the necessary resources for proper evidence packaging.
  • Technology and Timeliness: Rapid advances in technology and delays in evidence transportation can affect evidence integrity. Jurisdictions should prioritize updating procedures and streamlining processes to mitigate these risks.

Prioritizing Evidence Integrity

  • Resource Allocation: Jurisdictions must allocate sufficient resources, advocating for the necessary funding and support to maintain evidence in conditions suitable for future analysis. This includes prioritizing the security, packaging, and storage of biological evidence.

Managing Wet and Dry Evidence

  • Wet Evidence: Biological evidence that is inherently liquid or wet at collection must be appropriately managed. While some samples, like blood draws, remain liquid, other wet evidence should be dried before long-term storage to prevent microbial growth.
  • Temporary Storage: In situations where immediate drying isn’t feasible, wet evidence should be temporarily stored in impermeable, nonporous containers and refrigerated at 2°C to 8°C. This prevents degradation until the evidence can be properly dried.
  • Drying Techniques: Properly drying wet evidence is crucial. Low-tech solutions, such as using designated biohazard lockers or shower stalls for air drying, can be effective for agencies with limited resources. Larger departments may employ high-tech methods with specific drying equipment.

Decontamination and Repackaging

  • Decontamination: To prevent cross-contamination, surfaces and items used in the drying process should be decontaminated with a solution like 10 percent bleach. It is advisable to consult with a laboratory on suitable cleaning agents.
  • Repackaging Dried Evidence: Once dried, evidence should be repackaged in new, dry materials. For garments, sterilized paper placed beneath and between items during drying should also be packaged and submitted, as it may contain valuable trace evidence.


The effective packaging and storage of biological evidence are foundational to forensic investigations. By implementing best practices and ensuring that evidence handlers are equipped with the necessary resources, jurisdictions can significantly enhance the reliability of forensic analysis, supporting the pursuit of justice.

🔍 Reflect

How do the challenges of packaging and storing biological evidence underscore the importance of ongoing training and resource allocation within forensic evidence management?

Liquid and Tissue Evidence

Handling, packaging, and storing liquid and tissue evidence require specific protocols to ensure the integrity of these materials for forensic analysis. This section outlines the best practices for managing such evidence, from blood samples to extracted DNA, emphasizing the importance of preventing contamination, degradation, and ensuring safety.

Blood Samples

  • Packaging and Labeling: Blood draw tubes and vials, typically supplied by crime laboratories or hospitals, should be contained in easily identifiable packaging. Unmarked vials received by a department must be placed in envelopes clearly labeled with contents and marked with a biohazard symbol. Glass vials containing blood should never be frozen due to the risk of breaking.

Hypodermic Needles

  • Safe Storage: Needles and other sharps must be stored in puncture-resistant, leak-proof, and properly labeled containers. These items should be segregated from other evidence types to prevent injury and potential infection.

Breathable Storage Containers

  • Advantages: Breathable containers are crucial for storing biological evidence, as they allow air circulation, preventing condensation and subsequent bacterial growth that could compromise DNA integrity.

Urine Samples

  • Identification and Storage: Like blood samples, urine vials not clearly labeled upon receipt should be appropriately packaged and marked. These biohazards require separate storage in a designated area, following safety protocols to avoid exposure risks.

Sexual Assault Kits

  • Management: Provided by various institutions, sexual assault kits require meticulous documentation and storage. Uniform-sized boxes and envelopes enhance efficiency in storage and retrieval, with long-term preservation necessitating controlled environmental conditions to prevent evidence degradation.

Extracted DNA

  • Preservation: Traditionally stored frozen or refrigerated, extracted DNA’s stability is vital for future testing. The costly nature of maintaining cold storage has prompted research into room temperature preservation methods, aiming to balance cost-effectiveness with DNA extract integrity.

Tissue Samples

  • Long-term Preservation: Post-analysis, tissue samples are usually stored at -20°C to prevent degradation. In mass casualty situations or when immediate freezing is impractical, preservation reagents may temporarily stabilize samples at room temperature until proper storage solutions are available.


The meticulous care in packaging, labeling, and storing liquid and tissue evidence is fundamental to forensic science. Adhering to established protocols ensures the safety of those handling the evidence, maintains the evidence’s integrity for analysis, and supports the justice system’s needs. As technology and methodologies advance, continuous evaluation and adaptation of evidence management practices will be necessary to meet the evolving demands of forensic analysis.

🔍 Reflect

How do evolving technologies and methodologies impact the protocols for packaging, storing, and preserving liquid and tissue evidence in forensic science?

Optimal Environmental Conditions

The preservation of biological evidence is critical for forensic analysis, requiring careful attention to drying, packaging, and, crucially, storage under appropriate environmental conditions. These conditions are essential to maintain the integrity of the evidence and prevent degradation. Here’s an overview of the recommended storage environments for various types of biological evidence, reflecting the need for precise temperature and humidity control.

Recommended Storage Conditions

  • Frozen Storage: For evidence that necessitates freezing, a temperature at or below –10 °C (14 °F) is maintained. This setting is ideal for preserving DNA in tissues, blood samples, and other biological materials that are particularly susceptible to degradation.
  • Refrigerated Storage: Refrigeration, with temperatures between 2 °C and 8 °C (36 °F and 46 °F) and less than 25% humidity, is suitable for liquid samples like blood and urine that require cooler temperatures without the risk of freezing.
  • Temperature-Controlled Storage: Some evidence can be stored effectively at temperatures between 15.5 °C and 24 °C (60 °F to 75 °F) with less than 60% humidity. This environment is conducive to the preservation of items that need to be kept cool and dry but do not require refrigeration.
  • Room Temperature Storage: For evidence that does not require strict temperature control, room temperature storage is adequate. However, it is important to ensure that the storage area is protected from direct sunlight, excessive heat, and moisture, even in these less controlled environments.

Distinguishing Between Temporary and Long-Term Storage

  • Temporary Storage: Defined as storage for 72 hours or less, temporary storage is often utilized when the proper long-term facilities are not immediately available. Medical facilities, law enforcement property rooms, and transport vehicles serve as temporary holding areas. The key is to ensure that even in temporary storage, evidence is protected from adverse conditions that could compromise its integrity.
  • Long-Term Storage: Any location where evidence is stored for more than 72 hours is considered long-term storage. These facilities are equipped with the necessary environmental controls to ensure the preservation of evidence over time. Long-term storage requires meticulous monitoring of temperature and humidity to protect the evidence from degradation.

The strategic storage of biological evidence under optimal environmental conditions is a cornerstone of forensic science. By adhering to recommended storage guidelines, forensic professionals can ensure the preservation of evidence integrity for future analysis. As forensic techniques evolve, so too will the standards for evidence storage, necessitating ongoing vigilance and adaptation to safeguard the crucial links that biological evidence provides in the pursuit of justice.

🔍 Reflect

How do the challenges of maintaining proper environmental conditions for evidence storage underscore the importance of infrastructure and resource allocation in forensic evidence management?

References and Further Reading


Modification History

File Created:  05/02/2019

Last Modified:  04/05/2024

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