Fresno Criminal Defense Attorney  | Fresno DUI Defense Lawyer | Understanding Serology and Biological Evidence Part 6

Using blood evidence in a crime scene reconstruction

The study of serology that is important for criminal defense attorneys to understand.  Understanding what various fluids in the bodies do, how they react, and other behaviors that are dependent upon the characteristics of the fluid in question.  Viscosity is an important factor, and the actions of a falling drop of liquid depend greatly upon the viscosity and properties contained in the fluid.

Hemodynamics

Blood is a viscous liquid circulated through the vasculature of the body by the heart, and functions to deliver nutrients and oxygen to the cells of our body and to facilitate the removal of waste products. Blood carries glucose and hormones to our tissues and plays a critical role in the body's defenses by supporting antibodies and white blood cells that remove foreign particles from our systems. The heart, which essentially functions as a hydraulic pump, pushes blood out through the main artery called the dorsal aorta. The dorsal aorta divides and branches into many smaller arteries that supply each region of the body with freshly oxygenated blood. Arteries have very muscular walls with strong elastic properties; an inner wall of epithelial cells lines the inside of the arterial wall which makes it extremely smooth and allows the blood to flow unimpeded. The muscular walls of arteries expand and contract as they fill with blood and push the fluid under high pressure throughout the vascular system. The rhythmic pumping of the heart combined with the contractile forces of the arteries circulates the blood efficiently.

As arterial branches divide further and further they form capillaries. Compared to arteries (and veins), capillary walls are only one epithelial cell thick and are quite fragile. Blood cells can only flow through capillaries in single file while oxygen, carbon dioxide, nutrients and waste products diffuse back and forth across the capillary wall to, and from, the surrounding tissues and organs. Capillaries deliver deoxygenated blood and waste products to the veins for transport back to lungs for re-oxygenation and back to the heart for recirculation.

The venous system is much less elastic than the arterial system so blood is transported back to the heart under much less pressure. Valves positioned along each vein prevent the backflow of blood and keeps it moving in one direction against the force of gravity (think about blood flowing from the foot up towards the lungs and heart). 

Oxygenated blood in arteries is very bright red in color, whereas deoxygenated blood in veins is a darker purplish-red color, and may appear blue as it passes through veins close to the surface of the skin.

Blood is commonly used for the prosecution and defense of violent crimes, and other instances for crime scene recreation.  A proper understanding of the issues that could be presented in court can help a criminal defense attorney prepare the best possible defense.  Spotting the issues is important, and this education allows me to be better able to defend my clients when blood evidence is expected to be presented by the prosecution, and also to present the evidence in defense of my client.

Clot Formation and Bruising

Since the body can only function when the cells receive enough oxygen, it has ways of protecting itself when blood loss occurs. The body responds to blood loss by increasing vasoconstriction and fluid retention, and platelet cells circulating in the blood become activated. Platelet activation initiates a cascade clotting reaction at the site of an open wound. Platelets are irregularly shaped, colorless cells with sticky surfaces that gather at a wound site, and through a series of reactions involving calcium, vitamin K and the protein fibrinogen, form a clot that will stop the bleeding. When blood is exposed to air the platelets begin to break apart and react with fibrinogen to make fibrin threads. These fibrin threads form a mesh-like web that traps blood cells and dries to form a clot or a scab. Clot formation requires the interaction of calcium and vitamin K and insufficient or reduced amounts can result in abnormally slow, life threatening, clotting rates. Scabs are external blood clots, but internal blood clots can also form that may be life threatening if they break away, travel in the circulating blood, and become wedged in a major blood vessel supplying the heart or brain. Normal clotting time for blood outside the body ranges from 3 to 15 minutes in healthy individuals. Bruising is the result of bleeding under the skin when superficial blood vessels are damaged. The color of a bruise changes with age; fresh bruises are usually blue-black and fade to green-yellow over a couple of days.

Many of the domestic violence cases that occur are based upon apparent bruising on the victim, or at times, on the accused.  Fresno County courts will often present pictures of injuries, where the victim claims that the injuries occurred at a specific time or date.  Many times proper education on the subject of bruising will allow a defense attorney to see that color photos and see the color pattern present present a different inference than that which was alleged.  Bruises change over time, and their appearance can be critical in a criminal defense case.

Bloodstain Pattern Analysis

The shape and distribution of blood drops at a crime scene can be used to help reconstruct how a crime occurred. In 1971, MacDonell outlined several general rules regarding blood spatter evidence. Blood spatter is a tool that can be used to help an investigator determine what may have taken place at a crime scene.

Violent assaults, murder, homicides, and battery charges often include physical evidence of the bloodstains and blood spatter.  This is important in defending allegations, and can also be used in defense of a person accused of these crimes.

Physics of Blood Spatter

Because of the viscous nature of blood, the behavior of a blood spot subjected to an external force can be predicted. A blood drop is held together by cohesive forces that produce a surface tension within and on the external surface of the drop. Surface tension is the force that pulls the surface molecules of a liquid together, decreasing the surface area of the drop and forms a skin that helps the liquid resist penetration. The surface tension of blood is less than that of water. To create blood spatters, the surface tension of a blood drop must be overcome from an applied external force.

When falling through the air, the molecular cohesive forces acting upon the surface of the blood drop, cause it to become spheroidal in shape. A passive drop of blood in air (such as blood dripping from a small wound) occurs when the volume and mass of a drop increase to the extent that the gravitational pull on the drop overcomes the cohesive forces at the blood source.

The amount of blood needed for a passive drop to form depends on the type of surface and the surface area from which the blood originated. An average volume of drop of blood is about 0.05 ml, which forms a spheroid about 4.56 mm in diameter while in the air. The more viscous a fluid becomes, the more slowly it flows; blood is six times more viscous than water and has a slightly higher specific gravity than water. The viscosity and specific gravity of blood are responsible for the stability of exposed blood drops and their resistance to alteration or disruption.

A blood drop falling through the air will accelerate until the forces opposing the drop equal the force of gravitational pull, and the drop reaches terminal velocity. According to MacDonell, the average terminal velocity speed for a falling blood drop of blood is 25.1 feet /second, reached in a maximum falling distance of 20-25 feet. When a falling blood stain strikes a surface, the resulting spot acquires a diameter that varies with the volume of the drop, the texture of the surface it impacts and to some degree, the distance fallen.

Uniformly sized blood drops, dropped from different heights onto a smooth hard surface will produce bloodstains with increasing diameters. Dropped over a range of 6 inches to 7 feet the diameters of the resultant spots range from 13 to 21 mm. At heights greater than 7 feet, the diameter doesn't change significantly.

Target Surface

To create a smaller blood spot from a parent blood spot, the outer skin or surface tension of the parent spot must be broken. It doesn't matter how far a blood spot falls; it will not divide into smaller spots unless it strikes a surface. The force of striking the surface overcomes the surface tension of the falling spot. Generally a smooth, hard, non-porous surface like glass will create much less (if any) spatter compared to a rough textured surface like wood or concrete. Rough surfaces have protuberances that rupture the surface of the drop, producing spatter and irregular stains with spiny and serrated edges.

Directionality

Geometric stain parameters are used by analysts to determine the direction of flight before a blood drop impacted an object or surface. These parameters are derived from the stain edge characteristics of individual stains and can provide useful information. The narrow end of an elongated bloodstain usually points in the direction of travel. Once the directionality of blood staining has been determined, a point of convergence that represents the relative location of the blood source can be determined by joining straight lines drawn through the long of axis of each stain.

Area of Origin

The point of origin of a blood source may be determined by establishing the impact angles of individual bloodstains and their trajectories. By extrapolating back to a common axis at 90° up from the two dimensional area of convergence, the approximate location the blood source was when it was impacted, can be estimated three dimensionally.

Angle of Impact

If the angle of impact of a falling drop is 90° then the bloodstain will usually be circular. Bloodstains striking a surface at an angle less than 90°are usually elliptical. The width and length of a stain are related to the angle of impact. If the length to width ratio is less than 1.0, the ratio is the sine of the angle of impact; therefore, the inverse sine is equal to the angle of impact.

Bloodstain Pattern Analysis

The shape and distribution of blood drops at a crime scene can be used to help reconstruct how a crime occurred. In 1971, MacDonell outlined several general rules regarding blood spatter evidence. Blood spatter is a tool that can be used to help an investigator determine what may have taken place at a crime scene.

Physics of Blood Spatter

Because of the viscous nature of blood, the behavior of a blood spot subjected to an external force can be predicted. A blood drop is held together by cohesive forces that produce a surface tension within and on the external surface of the drop. Surface tension is the force that pulls the surface molecules of a liquid together, decreasing the surface area of the drop and forms a skin that helps the liquid resist penetration. The surface tension of blood is less than that of water. To create blood spatters, the surface tension of a blood drop must be overcome from an applied external force.

When falling through the air, the molecular cohesive forces acting upon the surface of the blood drop, cause it to become spheroidal in shape. A passive drop of blood in air (such as blood dripping from a small wound) occurs when the volume and mass of a drop increase to the extent that the gravitational pull on the drop overcomes the cohesive forces at the blood source.

The amount of blood needed for a passive drop to form depends on the type of surface and the surface area from which the blood originated. An average volume of drop of blood is about 0.05 ml, which forms a spheroid about 4.56 mm in diameter while in the air. The more viscous a fluid becomes, the more slowly it flows; blood is six times more viscous than water and has a slightly higher specific gravity than water. The viscosity and specific gravity of blood are responsible for the stability of exposed blood drops and their resistance to alteration or disruption.

A blood drop falling through the air will accelerate until the forces opposing the drop equal the force of gravitational pull, and the drop reaches terminal velocity. According to MacDonell, the average terminal velocity speed for a falling blood drop of blood is 25.1 feet /second, reached in a maximum falling distance of 20-25 feet. When a falling blood stain strikes a surface, the resulting spot acquires a diameter that varies with the volume of the drop, the texture of the surface it impacts and to some degree, the distance fallen.

Uniformly sized blood drops, dropped from different heights onto a smooth hard surface will produce bloodstains with increasing diameters. Dropped over a range of 6 inches to 7 feet the diameters of the resultant spots range from 13 to 21 mm. At heights greater than 7 feet, the diameter doesn't change significantly.

Types of Spatter

Spatter is the random distribution of variably sized bloodstains produced by a variety of different mechanisms. The amount of spatter depends on the volume of blood present and the degree of force that was applied to cause the spatter. The amount of spatter produced is proportional to the amount of energy imparted on a stain, and will therefore vary between beating, stabbing and shooting incidents. 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 be taken when identifying the sources or causes of blood spatter. The type of spatter may reveal the mechanism through which the spatter was created.

Gunshot Impact Spatter

The form of spatter associated with gunshots is considered high velocity spatter, producing mist like spots that are less than 0.1 mm in diameter. Although smaller and larger spots are also encountered with gunshots, the size range depends on the amount of blood, the weapon caliber, the location, number of shots and the presence of clothing and hair. Similar impact spatter might be seen with other high velocity impacts like those resulting from explosions, machinery and high-speed vehicular injuries.

There are two sources of impact spatter related to gunshot wounds. At the entrance wound the impact spatter is known as blowback or back spatter and may be found on the weapon, and the assailant's hands or arms. When associated with a gunshot exit wound, the impact spatter is referred to as forward spatter.

Beating and Stabbing Spatter

Spatter associated with beatings and stabbings can usually be described as medium impact spatter. Again, a range of spatter diameters may be encountered depending on the type of impact and the amount of blood present. In these types 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 can be associated with consecutive blows. The type of weapon used will have an effect on the pattern produced, as will the number of blows in the assault. This type of impact produces spatter with 1-3 mm diameter as well as satellite and secondary spatter patterns resulting from blood dripping onto surfaces. 

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

Both blunt force trauma and knife wounds are some of the most common close quarters weapons used in criminal allegations.  Science has allowed us to understand how these injuries occur, and how the blood stain patterns are presented in many circumstances.  As a criminal defense attorney, this is important for helping my clients.

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 patterns. These patterns tend to be large and irregularly shaped, surrounded by small circular or oval satellite spatters (0.1 to 1 mm in diameter) around the periphery created by small spatters separating from the main bloodstain at the moment of impact.

Castoff Stain

When a body is beaten with a blunt object, blood doesn't often pool on the first blow. Consecutive strikes will impact on pooling blood and blood will likely transfer onto the weapon. As the weapon is swung back and forth, centrifugal forces will cast residual blood on the weapon onto any close by surfaces. These cast-off patterns are often linear stains that are larger than impact blood spatters. Sometimes the trails of castoff spatters can be used to estimate the number of blows that occurred during an assault, and whether the instrument was swung from the left or right hand side. These stains are typically seen in assaults using hammers and baseball bats.

Splashed Blood

Splashes occur when larger volumes of blood (> 1 mL) meet low velocity forces or fall freely to a surface. Splashes have large central areas and elongated peripheral spatters. Secondary spatter (ricochet) can occur when blood is deflected from one surface to another. If bleeding is severe enough, the movement of the victim or assailant can also produce splashing.

Projected Stains

Projected stains occur when blood is released when an impinging force exceeds gravity, producing peripheral spines and narrow streaking. Examples of projected blood include vomited blood, or patterns produced when someone runs through pooled blood.

Expirated blood

Blood that accumulates in the lungs or airways as a result of trauma 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 spatter resulting from medium and high velocity impacts. These stains may include air bubbles and may be diluted if mixed with saliva and nasal mucous.

Arterial Spurting

Depending on the size of the damaged artery, arterial leakage can range from small fine spray to gushing or spurting. 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.

Transfer Stains

Blood is transferred when a wet bloody object comes into contact with another object or surface, producing a blood transfer pattern that mirrors the original surface. Examples include patterns produced by bloody footwear, fingerprints, hairs, and fabrics. These types of stains often provide class or identifying characteristics.

Altered Stains

Several types of altered stains 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 after the initial attack. Coughing or exhalation of clotted blood from the victim may also be correlated with post injury survival time.

Wet bloodstains are especially susceptible to smearing, smudging and wiping by the assailant and victim. Changes in bloodstaining can also occur because of medical personnel treating the victim at the scene. Bloodstains can be diluted by rain, snow and other features of the environment as well as from cover-up attempts by washing and painting. Heat and fire can mask bloodstains or completely destroy them.

Clothing and Fabrics

When analyzing bloodstains, the clothing of an alleged assailant or suspect can provide important information. Analysis of stains on a garment can provide valuable information on how the blood was deposited there. Blood deposited passively includes transfer, flow patterns, saturation stains and drips. Blood deposited actively includes impact spatter, arterial spurts expirated stains and castoff. 

Weapons

Due to the effects of blowback and blood transfer, blood may be found on weapons such as guns and objects used in beatings. Stabbings using glass and knives may also result in blood transfer to the weapon. In some situations there may be a lack of blood on a knife that has been used as a murder weapon, this can occur when the blade is "cleaned" as it is pulled back out through the tissue layers of the body.

Recording Blood Spatter

In recording bloodstains and spatter, it's important to note the form color and size, the direction of splash, and the estimated height of fall. Photography is probably the best mechanism of recording and preserving the appearance of blood staining at a scene. Photographs should show the overall stain, and close up views should include a scale for comparison. Rough sketches can 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.

Fresno criminal defense attorney Jonathan Rooker prides himself on taking the time needed to gain the education on these subjects to help his criminal defense clients in a criminal court of law.

If you are accused of a crime, a science based defense may be the best defense that can be presented.