Fresno Criminal Defense Attorney | Blood Spatter Evidence

Spatter Stains-usually defined as the dispersion of small blood droplets due to the forceful projection of blood, is a random distribution of bloodstains of variable size produced by a variety of different mechanisms. Impact spatter is a bloodstain pattern created when a blood source is impacted with a blow or force resulting in the random dispersion of smaller drops.

The amount of spatter found on a target surface is directly related to the volume of blood available at the original source and the degree of force applied to that primary source to cause spatter. The amount of spatter and the resulting pattern produced is proportional to the amount of energy causing the spatter, and will therefore vary between beating, bludgeoning, stabbing and shooting assaults. As a form of physical evidence, all spatter patterns have class characteristics (those features that separate a class or group of like items from other classes or groups) that commonly indicate some kind of force was applied to a blood source; that the blood source separated into drops, and that the separated drops were distributed over flight paths and subsequently struck a target surface.

Methods of Description-When recording bloodstains and spatter patterns, it's important to note the form of the stain, any distinctive coloring, the size and the directionality of the spatter, and testimated height of fall if possible. Historically, blood spatter was categorized into three groups according to their associated impact velocities.  Many blood spatter experts today forego this conventional terminology due to the overlap of stain sizes between the groups.  Instead, once an analyst has categorized a bloodstain pattern as spatter, it may further be classified as impact spatter based on the size, shape and distribution of stains.

When using these terms to describe and characterize staining, it's important not to make premature assumptions about the cause of the impact. Because a stain is created by a high velocity impact, it does not imply that the stain was caused by a gunshot. Although a range of velocities and spatter sizes are presented, the characteristic ranges defined or considered by other analysts may vary slightly. Also note that the term velocity in this context applies to the injuring item or weapon and not to the speed of the blood droplets in flight.

Photography is probably the best mechanism of recording and preserving the appearance of blood staining at a scene and should be conducted as early as possible since sampling, presumptive testing, and scene processing can significantly change the information available. Photographs should show the overall stain, and when possible, a scale should be included in close up views for comparison purposes. Rough sketches may also be made to show the general appearance of stains in relation to other areas of the crime scene. Sketches should include the location, direction and size of the stain. 

Pattern Configuration-The type of spatter produced from impact mechanisms (such as beating or gunshot) will differ from those caused by projection mechanisms like cast off stains and arterial spurting. Occasionally stains will show characteristics relating to both mechanisms, so care must always be taken when identifying the sources or causes of blood spatter. Any kind of impact will produce a spatter pattern that includes stains covering a range of sizes; therefore, an investigator must be careful when choosing the size range to characterize the stain. By choosing stains that are larger or smaller the stain may be wrongly categorized. The investigator must characterize the stain pattern based on the most preponderant stain size.

Patterns associated with impact spatter tend to produce radiating patterns; the center of the radiation is the site where the blood source was impacted. The observed spatter pattern and individual stains will depend on the position of the impact point in relation to the target surface. Elliptical stains are often seen within patterns created when the target lies parallel to the primary direction of force within the impact. More spherical stains are observed when the target lies perpendicular to the force.

As patterns disperse and radiate out, the closer the site of impact is to the target and the more spatters we'll see per given area. As the droplets travel outward from the impact site the more distance we'll see between the stains as they follow their individual flight paths. Air resistance has an inverse effect on droplets based on their size. All droplets projected at the same speed will have different flight parabolas, with smaller drops encountering more air resistance and not traveling as far as larger droplets. This is an important point when investigating impact spatter from high velocity impacts. A spatter pattern is also influenced by the way an item impacts the contact site and the shape of the item or weapon; these parameters may affect how the blood ejects from the impact site, and the angle of the weapon impact may prevent spatter being distributed symmetrically.

Dispersion characteristics can be considered when determining the significance of spatter and lack of spatter on a person involved in creating a spatter producing event. The lack of spatter on a perpetrator may be due to being behind the zone of the radiating pattern where the level of dispersion is small. Lack of spatter does not prove the lack of presence at, or lack of participation in, a spatter creating event. 
Dispersion characteristics can also provide information that relates to the distance the spattered target was from the impact, and can also verify an object was in the proximity of an event.

Secondary and Satellite Spatters-A single drop of blood hitting a rough surface will produce small satellite stains (secondary spatter) around the parent stain. Blood dripping into blood on a horizontal surface will produce drip or splash patterns. These patterns are usually large and irregularly shaped, surrounded by small circular or oval satellite spatters or spines (0.1 to 1 mm in diameter) around the periphery. These are created as small spatters separate from the main bloodstain at the moment of impact. A splash pattern is a bloodstain pattern with diameter of 0.1 mm or more, created by a low velocity impact against a surface. Spines are the pointed edge characteristics that radiate away from the center of a bloodstain and their formation depends on impact velocity and surface texture.

Spatter and Contact Stains-Blood stains are often found on those individuals who discover or attend to a crime victim, as well as the perpetrator. Cradling, touching or moving a victim can result in the transfer of their blood onto clothing or skin. In some situations, light contact stains may actually appear to be spatter, leaving the analyst the job of distinguishing which stains are the result of violent dynamic spatter, and which result from gentle contact. When the whole pattern or a large stain is present it's easy to distinguish between the two stain types, but if only small amounts or partial stain is present then the task becomes more difficult. By viewing a contact stain on fabric under a low magnification stereoscope, the analyst can see blood traces on the upper surface of the weave of the fabric. Since the stain is the result of a wipe or a swipe, deeper areas of the fabric weave generally do not have any blood staining, even when compression contact may have taken place. When spatter strikes clothing, it hits the fabric surface in a projected fashion and small droplets permeate into the weave and can be found in deeper weave areas. Backspatter droplets from firearms are often found deep in the weave of fabrics.

Beating and Stabbing Spatter-Spatter associated with beating and stabbing incidents can largely be described as medium impact spatter. Once again, a range of spatter diameters may be encountered depending on the type of impact and the amount of blood present. In these kinds of assaults, the first impact with the weapon rarely produces a pool of blood. Only when a wound is opened will there be sufficient bleeding to produce pooling and further spatters associated with consecutive blows. The type of weapon used in the assault will have an effect on the pattern produced, as will the number of blows in the assault. This type of impact produces spatter with diameters in the 1-3 mm range as well as satellite and secondary spatter patterns resulting from blood dripping onto surfaces. 

In some situations multiple spatter mechanisms may be involved. Spatter resulting from a combination of beating, gunshot, arterial spurting, expirated blood and secondary and satellite spatter occur and the range of spatter seen with each form of impact will overlap to some degree, so it's important to consider all possibilities when making an interpretation of any blood spatter pattern.

Gunshot Spatter-Gunshot injuries commonly produce high velocity spatter. When the bullet hits the body sufficient force is applied to the wound to create spatter in the form of a fine aerosol. The form of spatter associated with gunshots is considered high velocity spatter, resulting in mist-like spots that are less than 0.1 mm in diameter. Generally the droplets created by this force radiate outwards in a three dimensional pattern called a cone. There are two sources of impact spatter related to gunshot wounds. The cone shape is formed in the original direction of the impact and creates a backspatter effect. Backspatter is blood spatter directed back toward the source of energy or force that caused the spatter and is often associated with gun shot entrance wounds. Blowback or backspatter resulting from an entrance wound from a near or contact shot, may be found on the weapon, and the assailant's hands or arms. Blood that travels in the same direction as the source of energy or force, and is often associated with gunshot exit wounds, is called forward spatter. Similar impact spatter might be seen with other high velocity impacts like those occurring as a result of explosions and machinery and high-speed vehicular injuries.

With forward and back spatter the conical pattern also follows the rules of dispersion. The closer to the target the more spatter produced. Spatter patterns very close to a target may lack dispersion and because of the size of the mist like droplets, may appear to be spray painted. The further from the impact, the more dispersed the pattern becomes with fewer mist like stains.

Although spots extending below and above the high velocity size are also encountered with gunshot, the size range depends on a number of factors including, the amount of blood, the weapon caliber, the location, the number of shots, and the presence of clothing and hair. It is not uncommon to find blood spatter stains ranging from 1-2mm in diameter interspersed amongst the mist like stains.

The creation of gunshot spatter has been attributed to the formation of a permanent wound cavity caused by the physical crushing of tissue as the bullet passes through. This action causes a temporary cavity to form in the wound making the tissues stretch and collapse back to their final damaged dimensions. Collapse of the temporary wound cavity usually occurs after the projectile enters and exits the site, leaving two sites from which blood can be ejected by the force of the collapse. When two or more successive shots occur, the first wound usually bleeds during the period between subsequent shots. The second shot impacts the body and the tissues surrounding the first wound compress making the wound squirt out its contents. This spatter is much heavier that that normally associated with a single gun shot. The closer the wounds are together, the more dramatic the squirting effect. Gunshot wounds may also force bloody tissue and bone out of the exit wound which can create stains of their own

Forward gunshot spatter patterns tend to be more symmetrical than backspatter, which are generally less defined; probably due to the primary force of the impact being projected in the direction of the projectile. In most cases the spatter from a gunshot wound cannot be predicted; sometimes the staining can be heavy and obvious, but at other times it may be limited or non existent. Head, chest, and heart wounds are difficult to predict, and spatter and spray can be limited by the presence of clothing and hair. These barriers to flight and the size of the spatter may make it difficult for an investigator to find. Dark surfaces, heavy fabric weaves, soil and vegetation can also mask very fine spatter. The absence of backspatter or blowback (the blowing back of blood and other tissue onto a firearm or shooter from a near contact or contact shot) depends on distance and the manner in which the weapon was held. These spatter droplets are so small they

can only travel about 4ft. It has also been suggested that these droplets are so fine they may dry immediately while suspended in air, resulting in a lack of staining on surrounding objects. Based on this theory, small droplets may also be carried in air currents and dispersed more than 4ft. from the source.

Expiratory Blood-Expiratory blood is blood forced from the mouth, nose or respiratory system under pressure (from coughing), resulting in spray or spatter. Blood that accumulates in the lungs or airways as a result of trauma to the mouth, nose, throat or lungs will be forcefully expelled through the mouth and nose of a living victim as part of a reflex process of clearing the air passages. This force produces a fine spatter similar to the kind of spatter resulting from medium and high velocity impacts. The spatter ranges from heavy, large stains to light, mist-like stains such as those found in gunshot situations and may be easily confused as such by the investigator.

Expiratory blood that mimics gunshot spatter is usually less vividly colored and may include air bubbles, or may appear diluted and watery when mixed with saliva and nasal mucous. Expiratory blood can usually be identified by correlating the position of the spatter with bleeding injuries observed in the appropriate body areas (mouth, nose and throat).

Fly Spots-Fly spots are bloodstains resulting from fly activity around a bloodied object. Although its not truly spatter, fly spots are often confused with other forms of blood spatter. Fly spots are created when flies at a crime scene feed on the blood. As they move around they track and regurgitate blood leaving small marks that may appear pattern-like. The blood specks are very symmetrical when regurgitated. These tracks are often found in warm areas where the flies rest, such as high window corners or sunny spots. The specks will test positive for blood with presumptive tests so investigators need to take care when evaluating these patterns.

Cast Off Stains-Cast-off patterns are bloodstain patterns created when blood is released or thrown from a bloody object while the object is in motion, or an object that suddenly stops its motion. Cast-off spatters can occur due to centrifugal forces as the bloody object is swung in an arc and from inertia at the end of a swing.

As the weapon is swung back and forth, centrifugal forces project blood present on the weapon onto any surfaces that come into close proximity. These cast-off patterns often form linear stains that are larger in size than impact blood spatters. These stains create linear patterns that are easily recognizable. The patterns created are not truly linear, since the arcing motion, the size and shape of the source item, and the amount of blood on the source item all contribute to the final pattern. In many situations the cast-off pattern trails can provide information on the minimum number of swings or blows that occurred during the event.

By reviewing the directionality of each stain we can estimate the number of forward and backward swings that occurred and whether the instrument was swung from the left or right hand side. Beating a body with a blunt object doesn't always produce pooled blood on the first blow, so investigators might add an additional blow to the estimate, assuming no blood was transferred on the first. Subsequent blows on a damaged body region will make contact with pooling blood and result in transfer of blood onto the weapon. These types of stains are typically seen in physical assaults using hammers and baseball bats.

Assault Weapon-The kind of item or weapon causing the castoff has a distinct effect on the resulting stain pattern. A broad object, or an object that has more than one surface, will create a pattern that is different from the pattern created by an object with a sharp or single edge or a smooth surface. Sharp edged weapons characteristically cast stains that very linear with small spatters. Bats and clubs which have a larger surface area tend to create larger stains and wider patterns. A board or 2x4 plank creates a very broad, characteristic pattern with disperse stains that might seem to be the result of multiple events. Usually, an analyst can determine if more than one swing or event occurred and whether the observed pattern is the result of a single cast-off or several cast-offs.

Blood Volume-The volume of blood transferred to the weapon during a cast-off event will also affect the number and size of the resulting stains in the cast-off pattern. Regardless of the nature of the weapon, smaller amounts of blood will result in smaller stains, and the more blood available, the bigger the stains.

Castoff Stains: Orientation-Additionally, cast-off stains may provide information relating to the orientation and nature of the blow and whether the blow was applied from a left to right or right to left direction, possibly providing information relating to the hand in which the perpetrator held the weapon.

If there are several adjacent target surfaces that have staining (two adjacent walls and the floor and ceiling of a scene may contain spatter that is part of one event), examination of the spatter directionality may reveal the orientation and position of the perpetrator as the events unfolded. As the first swinging motion of the event occurs, the cast-off droplets may impact the first target surface at a 90° angle. As the swing continues, droplets are cast off of the weapon impacting the target at increasingly acute angles resulting in the formation of elliptical spatters. As the relative position of a target changes, like at the juncture of a wall and the ceiling, the angle of impact changes and spatter may revert to 90° impact characteristics.

Cast-off patterns can also provide information relating to the positioning of the victim during the assault. Staining may begin high on a target surface (an adjacent wall), and then move progressively lower (towards the floor). This type of pattern suggests the victim was in a standing position at the onset of the assault and then changed positions as the assault ensued. Cast-off patterns can also be created by blood cast off of the victim's arms, hands, or other appendages as they swing and flail about during an assault.

Weapons-Due to effects of blowback and blood transfer, blood can often be found on weapons such as guns and objects used in beatings. The drawback effect is blood that has been drawn back into the muzzle of a firearm. In a previous module we also discussed spatter caused by the entry and exit wounds of a bullet in forearms incidents.

Stabbing with glass and knives may also result in blood transfer to the weapon. In some situations however, there may be a lack of blood on a knife that has been used as a murder weapon, this can occur when the knife blade is “cleaned” as it is pulled back out through the tissue layers of the body.

Altered Stains-Several types of altered stains (stains that have been altered in some way from their original form) may be encountered in a crime scene investigation. Skeletonized bloodstains occur when a dried bloodstain begins to flake in the center leaving a visible outer rim, or if the central area of a partially dried bloodstain is altered by wiping or some kind of contact. Clots of blood on clothing or at the scene may show drag patterns that suggest the movement of a body or the infliction of further injury sometime after the initial attack. Coughed or exhaled blood clots from the victim may also be correlated with a post injury survival time.

Wet bloodstains are especially susceptible to smearing, smudging, and wiping by the assailant and victim, and changes in blood staining may also occur as a result of the activities of medical personnel treating the victim at the scene. Bloodstains are also often altered and diluted by rain, snow and other environmental features as well as from cover-up cleaning and painting by the perpetrator. Heat and fire can mask bloodstains or completely destroy them.

A shadow, or void in a stain, is an area within a generally continuous bloodstain pattern that lacks bloodstaining. This phenomenon is also called ghosting. Voids typically show up in spatter patterns when another target surface overlays or intervenes with the primary target surface resulting in a void in the stain pattern on the primary target. This ghosting effect might suggest the nature of the object or the shape of the item creating the void. Again this type of staining might provide useful information on the movements or relocation of objects or items at a scene. Voids can usually be identified by the presence of abrupt and defined edges to the pattern, whereas stains that stop naturally do not have linear and well defined edges. Voids can be useful for establishing the body position of victims or the assailant during the time of the event. Voids on the victims clothing can indicate hands were raised in defense or the victim adopted a defensive position. When adopting the fetal position, the arms and legs of the victim will create a void on the main torso as they shield the body from a spatter event.

Other altered stains include the formation of a bubble ring. This is a ring produced when blood containing air bubbles dries and retains the bubble shape as a dry outline. Some bubbled stains can actually dry into three dimensional stains.

Movement and contact with wet stains can result in smears, smudges, and wipes. A smear is a large volume of blood, usually 0.5ml or more that is distorted so that further classification is impossible, this type of stain is similar to a smudge but is produced by a larger volume of blood. A smudge is a bloodstain that is so distorted that further classification is not possible. A swipe is the transfer of blood onto a surface not already contaminated with blood; one edge is usually feathered and may indicate the direction of travel. This is the type of stain created by hair swipes. A wipe is the bloodstain pattern created when an object moves through an existing bloodstain. The object removes blood from the existing stain, and alters its appearance.

Projected Blood-Projected stains occur when blood is released or projected in large volumes when an impacting or impinging force exceeds the forces of gravity. Examples of projected blood include vomited blood, arterial spurting, or patterns produced when someone runs through pooled blood. These stains are generally associated with the production of peripheral spines and narrow streaking that are indicative of the force behind the stain created and the force with which the droplets hit the target surface. Ricochet is the deflection of large volumes of blood after impact with a target surface that results in stain formation on a second surface. This type of staining is also called secondary splash, but does not occur when small drops of blood strike a surface.

Arterial Spurting-Arterial spurting produces bloodstain patterns that are characteristic of blood exiting the body under pressure from a breached artery or the heart. These patterns have spurt like characteristics indicating a system under pressure, or reflecting the pressure fluctuations of the circulatory system, or both. Depending on the size of the damaged artery, arterial leakage can range from small fine spray to gushing. The amount of blood produced depends on the severity of the damage, the size of the vessel, position of the victim and the presence of clothing. Uninhibited arterial spurts usually involve large volumes of blood. The presence or absence of arterial spurts can provide important information on the physical status of the victim. A live victim with a breached artery can produce projected stains with significant volume. If these types of stains are lacking, or weaker or erratic patterns of spurting are observed, the victim may have been dead or have a decreased heart rate when the artery was breached.

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