When is it more appropriate to use presumptive tests in a crime investigation? When is it more appropriate to use confirmatory tests in a crime investigation? Why is hemoglobin important for presumptive tests for the presence of blood?Describe how the Kastle-Meyer test is used to detect blood at a crime scene.

Phenolphthalein is a presumptive test that reacts with the heme molecule present in blood. A positive reaction gives a pink color. While bloodstains normally appear red-brown in color, the color of the substrate or the age of a stain may affect the appearance or visibility of the stain.

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