Death and the maiden

Distinguishing between stamping in blood from walking through blood using blood pattern analysis

Bloodstains are typically encountered in violent incidents involving the use of a weapon or physical actions, such as punching, kicking, or stamping. Bloodstain pattern analysis can provide inceptive evidence or intelligence about what happened in an alleged incident, the sequence of events, along with indicating possible suspects if blood is analysed through DNA profiling. This research project focused on the differences in patterns created on footwear during a violent action, such as stamping on a person, and a non-violent action, such as walking through a pool of blood. In this project, several experiments were designed to simulate the stamping and walking actions on a surface wet with blood: carpet, lino flooring, and belly pork meat. Two volunteers with varying body weights were recruited to perform the two actions, using a pair of trainers and a pair of Wellington boots. Defibrinated horse blood was used to simulate real human blood. It was found that the patterns created from stamping and walking through blood differed by the type of pattern and the number and size of stains. The footwear used in the stamping action was characterised by a larger contact stain on the sole than those used in the walking actions: ∼209 mm in length by ∼92 mm in width versus ∼65 mm in length by ∼60 mm in width. The stamping action produced a large number of impact spatters (∼435) on the sides of the footwear versus no impact spatters in the walking actions. The presence of impact spatters was found to be the most prominent feature that differentiated between the two actions. The findings were statistically significant (p < 0.05) and could assist in evaluating whether a defendant was actively involved in a stamping action, or the evidence found was due to innocent reasons.

Characterising the dynamics of expirated bloodstain pattern formation using high-speed digital video imaging

During forensic investigations, it is often important to be able to distinguish between impact spatter patterns (blood from gunshots, explosives, blunt force trauma and/or machinery accidents) and bloodstain patterns generated by expiration (blood from the mouth, nose or lungs). These patterns can be difficult to distinguish on the basis of the size of the bloodstains. In this study, high-speed digital video imaging has been used to investigate the formation of expirated bloodstain patterns generated by breathing, spitting and coughing mechanisms. Bloodstain patterns from all three expiration mechanisms were dominated by the presence of stains less than 0.5 mm in diameter. Video analysis showed that in the process of coughing blood, high-velocity, very small blood droplets were ejected first. These were followed by lower velocity, larger droplets, strands and plumes of liquid held together in part by saliva. The video images showed the formation of bubble rings and beaded stains, traditional markers for classifying expirated patterns. However, the expulsion mechanism, the distance travelled by the blood droplets, and the type of surface the blood was deposited on were all factors determining whether beaded stains were generated.

Using oral microbial DNA analysis to identify expirated bloodspatter

Distinguishing expirated bloodstains (blood forced by airflow out of the nose, mouth or a chest wound) from impact spatter (blood from gunshots, explosives, blunt force trauma and/or machinery accidents) is an important challenge in forensic science. Streptococcal bacteria are only found in the human mouth and saliva. This study developed a polymerase chain reaction (PCR) method that detects DNA from these bacteria as a sensitive tool to detect the presence of saliva. The PCR method was very specific to human oral streptococci, with no PCR product being made from human DNA or DNA from other microbes that were tested. It was also very sensitive, detecting as little as 60 fg of target DNA. The PCR amplification gave product with 99 out of 100 saliva samples tested. PCR was not inhibited by the presence of blood and could detect target DNA in expirated bloodstains in a range of materials and for up to 92 days after deposit on cardboard or cotton fabric. In a blind trial, the PCR method was able to distinguish three mock forensic samples that contained expirated blood from four that did not. Our data show that bacteria present in the oral cavity can be detected in bloodstains that contain saliva and therefore can potentially be used as a marker in forensic work to distinguish mouth-expirated bloodstains from other types of bloodstains.

PCR-based detection of salivary bacteria as a marker of expirated blood

Distinguishing between bloodstains caused by a spatter pattern or by expirated blood may be crucial to a forensic investigation. Expirated blood is likely to be contaminated with saliva but current techniques have limited sensitivity, especially with small bloodstains. We report that a PCR assay, designed to detect salivary bacteria, can amplify streptococcal DNA from saliva stains applied to fabrics for at least 62 days after seeding. Bacterial DNA was detected when 0.01 microl of saliva was present in the stain and the amplification was not affected by contamination with blood. These findings indicate that PCR amplification of salivary microbial DNA may have application in the identification of expirated bloodstains in forensic case-work.