This document discusses three key questions to determine if a substance found at a crime scene is blood, and if so, whether it is human blood and how it compares to a victim or suspect's blood. It outlines several presumptive blood tests, including the Kastle-Meyer test using phenolphthalein and hydrogen peroxide, which turns pink in the presence of blood, and the Leucomalachite green test which turns blue-green. While generally reliable, these tests can produce false positives from substances like potatoes and horseradish. The document also describes the luminol test, an alkaline solution that emits a blue light in the presence of blood but can be affected by bleach, metals or some