It is important that first responding officers at crime scenes understand the importance of blood spatter evidence and properly measure and photograph that evidence for blood spatter experts to analyze. The principles and procedures necessary to correctly collect blood spatter evidence are not difficult to learn and may reveal important information regarding the crime. While the information on how to measure and photograph blood spatter evidence may be learned in a 2-day training course, it is also important that first responding officers have a basic understanding of what blood spatter evidence indicates. The article describes the three classifications of blood spatter velocity and what they mean (high, medium, and low), as well as how to tell which way the blood traveled. The velocity of the blood spatter is a good indication of the speed of the force that sent the blood in motion, suggesting the type of weapon used on the victim. By measuring the direction the blood traveled it is possible to pinpoint where the victim was at the time of the attack. By simply learning how to measure and photograph important blood spatter evidence for later analysis by experts, police officers may significantly add to their knowledge of the circumstances of the crime under question. Figures, endnotes