Forensic science is one of the most important pillars used to understand the facts and events of the crime, through the analysis of crime scene evidence and reconstruction of crime events that will help investigators to solve crime cases, through certain documentation procedures and collection of materials available at the crime scene and through which clues are identified that can lead to arresting the perpetrator of the crime or identifying the victim or know what happened at the crime scene. In this context we will focus on how we can detect the presence of blood at the crime scene, this test will help differentiate blood from other substances, which will save time, effort and even costs by transferring many samples to the laboratory to examine the presence of blood using some crime scene tests that will indicate the presence of blood. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay There are three commonly known tests that can be applied at the crime scene, the leucomalachite green (LMG), the phenolphthalein Kastle Meyer (KM), and the luminal test. These three tests can give us a quick result on the presence of blood at the crime scene. We will explore in detail one of those methods that can be used at the crime scene. Kastle Meyer (KM) test The Kastle Meyer (KM) test is a rapid, simple, reliable and inexpensive forensic test for the presence of blood, it is sensitive, specific and consumes the smallest possible amount of sample. The Kastle Meyer (KM) 3-step test has been used for decades as a rapid, presumptive test for blood. The test identifies the heme component of hemoglobin, which in the presence of hydrogen peroxide catalyzes the oxidation of the phenolphthalein indicator, turning it pink. Materials and procedure: To apply the test it is necessary to provide materials as follows: 70% Kastle-Meyer solution ethanol distilled or deionized water 3% hydrogen peroxide cotton swabs or filter paper dropper or pipette. Procedure Add a few drops of distilled water to the paper exchange or filter paper and gently rub only a small amount as needed onto the dried blood sample. Then use 2 drops of 70% ethanol on the exchange or filter paper to increase the sensitivity of the test, no reaction agrees. By adding 1-2 drops of KM (phenolphthalein) solution, the exchange or filter paper should now be colorless or pale. By adding 1-2 drops of a 3% hydrogen peroxide solution at this stage the exchange or filter paper should immediately turn pink, which will indicate a positive test for the presence of blood. This chemical reaction can help instantly distinguish blood from another substance. False positive For the KM test the result must be negative and positive, as we now know if the sample turns pink this will be an indication of the presence of blood so if the sample does not show any color change instantly, this means that it has not been detected blood, although if the sample is kept for approximately 30 seconds there will be a color change due to the reaction even if no blood is present. This is the result of hydrogen peroxide oxidation of phenolphthalein in the indicator solution. This test will also give false positive results, for example as we mentioned above if there is no blood the sample will turn pink after a while, this is due to the chemical reaction of the presence of oxidant and can be found in broccoli or cauliflower this is an important fact that should be taken into consideration by the forensic team at the crime scene. A.