Quality control of evidence

DEFINITION: Documented and demonstrable processes and procedures used to ensure the integrity of all items of evidence.

SIGNIFICANCE: Demonstrable procedures for the collection, packaging, handling, transport, examination, and storage of items of evidence are crucial to ensuring that those items retain their evidential value. It is of the greatest importance that confidence can be placed in the integrity of an evidential item and any findings derived from it.

Quality-assurance programs have become commonplace in forensic organizations, and a number of accreditation bodies have been formed for the purpose of assessing the performance of forensic organizations against strict standards of practice. Accreditation allows organizations to demonstrate that they have been assessed and that their procedures were found to be satisfactory. They must also be able to demonstrate that those procedures are put into practice, however.

One of the most significant parts of any forensic organization’s quality-assurance, or accreditation, program is that relating to the handling of evidence. The organization must be able to demonstrate that each item of has been handled appropriately from the moment of its discovery up to its presentation in court for trial, and sometimes through subsequent appeals and retrials. If it can be demonstrated that an evidential item has been, or may potentially have been, compromised or contaminated in some way, the significance of its evidential value becomes questionable. Doubt about the handling of a single piece of evidence may also call into question the evidential value of any items held or handled in any way by the same specific laboratory or individual. This may also have ramifications for other cases involving that laboratory or individual.

Scene Security

When personnel take control of a crime scene, they have a responsibility to take all reasonable steps to protect all potential evidence at the scene from deleterious change. Initially this involves ensuring that appropriate scene boundaries are put in place, a task that can be logistically difficult, particularly when a scene is outdoors.

After the scene parameters are in place, law-enforcement authorities must maintain control of the area to prevent entry to the scene by anyone other than those strictly required for processing and recording of the scene. Wherever possible, those individuals should all be well-trained, competent, and experienced personnel.

Chain of Custody

When an item of potential evidence is identified, its location within the crime scene and its conditions must be recorded. This is typically done through photography, scene sketches, and general notes. After possession is taken of the item, it becomes part of an official exhibits register.

The exhibits register, or evidence log, is a list of all items that come into the possession of the police, whether collected from a scene or by other means, in relation to an investigation. The register typically assigns a unique identifier to each item and records a description of the item along with information concerning where it was found and by whom and when it was physically seized. After an item is entered into the exhibits register, the register records the physical location of the item and every instance when custody of the item changes. In modern times, the evidence custody log may be digital.

During the course of an investigation, items may be transferred between sections of an organization or between organizations in order for required examinations to occur. Each section or organization should have its own process in place for recording the chain of custody of any items within its possession. A complete evidence log not only documents who had custody of items and when, it also proves that the evidence was not handled by people not approved to do so.

The Importance of Packaging

The method of packaging of an item of evidence is also crucial to maintaining its evidential value. Inappropriate packaging may destroy evidence. For example, the (deoxyribonucleic acid) in biological fluids can rapidly degrade if stored in a moist environment, such as inside a sealed plastic bag; such evidence should therefore be stored in breathable packaging, such as paper bags. Flammable liquid residues in a fire debris sample, in contrast, should not be packaged in paper, as this allows them to evaporate; such residues should be packaged in airtight containers. It is important that all personnel who handle evidential items understand how packaging can affect the items and thus potentially affect the results of subsequent analyses.

Item Examination and Preservation of Item Integrity

During the laboratory examination of items of evidence—whether they are bullet fragments, bloodstains, or articles of clothing—some degree of physical handling of the items is inevitable. Following examination of an item, it is the responsibility of the examiner to be able to demonstrate that all reasonable steps were taken to ensure that the item was not detrimentally affected by the examination any more than was strictly necessary to perform the examination properly.

Crime laboratories often have strict requirements in place detailing what is considered to be acceptable practice in the examination of evidence. For example, the examination of items for DNA, particularly trace or contact DNA, can often involve elaborate precautions to prevent contamination. Examination spaces need to be thoroughly cleaned before and after items are examined. All equipment used must be either disposable or able to be cleaned thoroughly between item examinations. Examiners must wear disposable lab coats and gloves, face masks, and hair coverings to minimize their DNA contribution. This protective clothing must also be completely changed between the examinations of different items.

Records are kept of when an item was examined, who the examiner was, and where the examination took place. Any tests performed on an item are also recorded, as are the details of any subsamples collected.

Examination strategies for items involved in an investigation should also be considered. For example, if practical, a crime lab might schedule examinations of items from complainants, suspects, and scenes in a particular case to take place in different examination rooms on different days and by different analysts. This sort of strategy effectively eliminates any reasonable suggestion of cross-contamination occurring between case items.

Bibliography

Adams, Thomas F., et al. Crime Scene Investigation. 2nd ed., Prentice Hall, 2004.

Badiye, Ashish, Neeti Kapoor, and Ritesh G. Menezes. "Chain of Custody." National Library of Medicine, 13 Feb. 2023, www.ncbi.nlm.nih.gov/books/NBK551677/. Accessed 16 Aug. 2024.

Fenoff, Roy, et al. Crime Scene Investigation, 4th ed, Routledge, 2022.

Fisher, Barry A. J., and David R. Fisher. "Physical Evidence Collection." Techniques of Crime Scene Investigation. 9th ed. CRC Press, 2022, pp. 43-51.

Inman, Keith, and Norah Rudin. Principles and Practice of Criminalistics: The Profession of Forensic Science. CRC Press, 2001.

Pyrek, Kelly M. Forensic Science Under Siege: The Challenges of Forensic Laboratories and the Medico-Legal Investigation System. Elsevier Academic Press, 2007.

Saferstein, Richard. Forensic Science: From the Crime Scene to the Crime Lab. 3rd ed., Pearson, 2016.

St. Clair, Jami J. Crime Laboratory Management. Academic Press, 2002.