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The principles associated with bloodstain recognition and analysis are simple enough that all officers and detectives can quickly grasp them. Although this article can never replace advanced bloodstain instruction, officers and detectives can still incorporate this information into their respective patrol and investigative job functions.
The levels of force associated with bloodstain analysis are broken down into three different categories. The first level: low velocity, often referred to as 90-degree spatter. At this level, drops of blood fall onto an object at a 90-degree angle, meaning gravity (the force) is stronger than the surface tension created by the blood’s cohesive forces, thereby causing drops to fall from the blood source. These stains are also sometimes referred to as dropped bloodstains.
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The second level: medium velocity. Medium-velocity spatter produces a pattern of bloodstains that measure 4mm–6mm in diameter or larger. A force of 5–25 feet per second (fps) impacting onto a blood source—e.g., punching, hitting, kicking, stabbing, stomping, etc.—produces medium-velocity spatter.
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The third level: high velocity. High-velocity spatter produces a mist or spray-type pattern consisting of bloodstain diameters of less than 1mm. A mist pattern of blood requires an impact force of at least 125 fps, such as gunshots, power tools and explosions.
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Swipe or Wipe The stain created when an object with blood on it moves across a surface, or when an item moves through an existing bloodstain or pool of blood. The swipe stain might be found when a body is moved or removed by dragging. The wipe stain might represent an attempt to clean the crime scene.
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Transfer The stain or pattern created when a bloodstained item comes into contact with a surface. Use the pattern of this stain to identify the object by studying the stain’s shape, size, pattern, design, etc.
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Void An area within a generally continuous bloodstain pattern that lacks stains. This interruption is caused by an intermediate target that disrupts the stain or blood pattern. Consider two important questions when you observe a void or transfer stain: 1) What object created the pattern? and 2) if the object has been moved or removed from the crime scene, why?
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Cast Off The stain pattern resulting from blood droplets that fly off of an object being swung or moved. These stains are often located on the ceiling within a scene where an assault took place. (For instance, blood drops strike the ceiling as the suspect raises the bloodstained weapon during repeated blows.) The location of these stains can often help you recreate the suspect’s position during the assault.
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Projected Blood Blood which impacts a surface under pressure. This stain most often represents arterial spurting, created by the breaching of an artery, a serious and life-threatening injury.
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Sequence of Events When two or more stains or patterns intermix with each other, assess each stain’s affect on the other. Example: 90-degree stains on a wipe pattern. 90-Degree Stains on a Wipe Pattern These bloodstains can allow you to determine a chronological order of events, which you can then use to attempt recreate or reconstruct the crime scene. Look at the 90-degree drops located within the wipe pattern in photo i. The fact that the drops appear to be undisturbed indicates the wipe pattern was present before the drops of blood struck the surface. A smearing of these same drops by the action that created the wipe pattern would indicate the opposite.
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Analyzing & Applying Now let’s get back to the crime scene sketched at the beginning of this article. Look at the stains present on the husband’s pants and shirt and try to identify them (see photos j, k, l and m).
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Analyzing & Applying Now let’s get back to the crime scene sketched at the beginning of this article. Look at the stains present on the husband’s pants and shirt and try to identify them (see photos j, k, l and m).
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Analyzing & Applying Now let’s get back to the crime scene sketched at the beginning of this article. Look at the stains present on the husband’s pants and shirt and try to identify them (see photos j, k, l and m).
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Analyzing & Applying Now let’s get back to the crime scene sketched at the beginning of this article. Look at the stains present on the husband’s pants and shirt and try to identify them (see photos j, k, l and m).
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