A novel experimental approach for classifying blood trails in relation to three different speeds of movement

Purpose When leaving a crime scene, bloodstained victims or offenders typically leave bloodstain patterns with a characteristic distribution and shape determined by the direction and speed of travel. The primary aim of this study was to examine whether shape and size characteristics of bloodstain patterns provide a method to accurately classify speed and arm movement. Material and methods In this study five subjects experimentally generated blood trails while moving over a distance of 10 m with a blood source mounted on the right arm. A tear-resistant paper placed on the ground captured the blood pattern. The subjects travelled this distance at three speeds (walking, jogging and running) and with two different associated arm movements (swinging arm versus non-swinging arm). Results By simple visual inspection characteristic geometric bloodstain pattern were identified: When moving slowly with a swinging arm, loop-like drip patterns, loops, were created. In contrast, slow movement with a non-swinging arm resulted in patterns resembling waves. The length and width of the loops and waves significantly increased in correlation with the step length (cm) and speed of motion (m/s). When analysis was limited to walking and running experiments, a significant, correct classification was achieved in 89% by including length and width (cm) of the loops and waves in a derived discrimination function. A new discriminant formula for differentiating between blood trails caused by walking and running movement is presented. Conclusion The analysis of the distribution and dimension of loop and wave-like drip patterns, including the speed of movement and biomechanical properties (i. e. arm movement) can greatly contribute to professional crime scene reconstruction.