Blood Evidence Collection, Processing, and Preservation in Forensic Investigation

Blood Evidence as a Forensic Tool

Blood evidence is an extremely valuable asset in criminal justice (Schiro, 2011; NIJ, 2000; OSP, 2002; NFSTC, 2013; Bestino, 2013). It has the unique and indisputable potential to solve a case or a crime, as it can accurately identify a participant or a victim. It can form a connection between a person and a criminal act, and can enhance or contradict witness testimony. Blood evidence also sets the investigator's direction in solving the case. When carefully documented, collected, and stored, it can be presented in court even years after the commission of a crime. Most importantly, blood evidence has the potential to implicate a particular suspect or to eliminate them from consideration entirely (Schiro, 2011; NIJ, 2000; OSP, 2002; NFSTC, 2013; Bestino, 2013).

The Role of Communication in Evidence Handling

To ensure the proper collection and preservation of this essential evidence, open communication must be established between the crime scene investigator and the forensic scientist (Schiro, 2011; Bertino, 2013; NIJ, 2002; OSP, 2002; NFSTC, 2013). The investigator should be thoroughly familiar with the capabilities of the crime lab, its preferred blood collection and preservation methods, the investigative information relevant to the forensic scientist, and the type of reference samples the lab requires. This information can change with technology, lab policies, personnel, or administration. A forensic scientist may also prefer a particular method of collection. It is therefore advisable for the investigator to confer regularly with forensic scientists to agree on suitable and efficient collection and preservation methods (Schiro, 2011; NFSTC, 2013; NIJ, 2002; OSP, 2002; Bertino, 2013).

The investigator must first determine the potential value of the blood evidence found and identify all potential problems in documenting, collecting, and preserving it (Schiro, 2011). Common problems include a lack of communication between investigators and forensic scientists, insufficient familiarity with the types of bloodstain pattern analysis, a lack of knowledge in determining which stains to collect for maximum useful information, poor reference samples, and the indiscriminate use of luminol at crime scenes. Luminol is a chemical that causes bloodstains to glow in the dark and must be used carefully to avoid compromising evidence integrity (Schiro, 2011).

Collection Methods for Blood Evidence

Blood evidence is usually present in violent and property crimes in the form of bloodstains (OSP, 2002). Bloodstains may appear red, brown, tan, or yellowish, and are often undetectable to the untrained eye. Blood is a valuable source of DNA, cells, and proteins, which can be examined to identify a perpetrator or victim. Laboratory tests can determine whether blood is present in a stain and whether that blood is human or non-human (OSP, 2002).

Collecting liquid or moist blood involves two separate procedures depending on quantity (OSP, 2002). If the blood to be collected is in a large quantity, the collector should saturate four to six sterile cotton swabs with the evidence, collecting a good mixture of clot cells and serum. The swabs must thoroughly air dry before being placed in a paper container, which is then properly labeled and sealed. If the quantity is small, only a limited number of swabs should be used to collect the blood one by one. These must also thoroughly dry before being placed in a labeled, sealed paper container.

If the bloodstained object can be moved, the whole item should be submitted intact. If it is not transportable, the blood may be collected by swabbing or by cutting out the stained area. Cutting is preferable when the stain has dried on an object such as car upholstery or carpet; a clean, sharp knife or scissors can be used to excise the stained area. The collector must take care to include unstained surrounding material as a substrate control and to prevent contamination of the stain. The excised sample should be packed in a paper container, properly labeled, and sealed in the same manner as other pieces of evidence (OSP, 2002).

Two additional collection methods are scraping and tape lifting (NFSTC, 2013). Scraping involves using a clean razor blade or scalpel to scrape the dried evidence onto a clean piece of paper, which is then folded and packed in a paper envelope. Dried bloodstains may also be collected using fingerprint lifting tape: the tape is placed over the stain and then lifted, transferring the stain to the adhesive side. The tape can then be applied to a clear piece of acetate and submitted to the laboratory (OSP, 2002).