Crime Library: Criminal Minds and Methods

Serology: It's in the Blood

Blood Pattern Analysis

Blood pattern analysis plays an important role in the reconstruction of many crime scenes. For example, when a prominent Cincinnati physician appeared to be the victim of an apparent suicide, the spatter pattern on his hand and on the couch on which he lay told a story of murder instead. The various types of bloodstains indicate how the blood was projected from the body via several factors:

  1. Type of injuries
  2. The order in which the wounds were received
  3. Whose blood is present
  4. The type of weapon that caused the injuries
  5. Whether the victim was in motion or lying still when the injury was inflicted
  6. Whether the victim was moved after the injury was inflicted
  7. How far the blood drops fell before hitting the surface where they were found

Blood may be dripped out, sprayed from an artery, oozed out through a large wound, or flung off a weapon raised to strike another blow. In the 1930s, Scottish pathologist John Glaister classified blood splashes into six distinct types:

  1. Drops on a horizontal surface
  2. Splashes, from blood flying through the air and hitting a surface at an angle
  3. Pools around the body, which can show if it's been dragged
  4. Spurts from a major artery or vein
  5. Smears left by movement of a bleeding person

Trails, either in form of smears when a bleeding body is dragged, or in droplets when it is carried. (Trails also form when a person is wounded and walks away but leaves blood along the way.)

Any of these can be traced back to their converging point by considering such factors as the surface on which it fell, the angle it hit, and the distance it traveled.

Brian Kennedy, a sergeant with the Sacramento County Sheriff's Department in California, is an expert in crime scene reconstruction, specializing since 1984 in bloodstain pattern analysis. For more than a decade, he has been teaching this technique to other forensic investigators and he believes that gaining insight from bloodstain patterns can strengthen interrogation strategies and provide juries with a clear visual format.  

"Bloodstain patterns," Kennedy says, "will help the investigators understand the positions and the means by which the victim and suspect moved, interacted, and struggled through the crime scene. With an understanding of what and how things occurred, investigators can focus and find fingerprints, footprints, hairs, fibers and other forms of trace evidence. The assessment of bloodstain patterns will also limit the need to collect an overabundance of redundant blood sample for DNA. Furthermore, a reconstruction of the scene helps the investigators determine which of the witnesses and suspects is telling the truth or lying."

The shape of the blood drop itself, according to Kennedy, can reveal significant information.  "The proportions of the drops can reveal the energy needed to disburse it in those dimensions. The shape of the stain can illustrate the direction in which it was traveling and angle at which it struck the surface. Choosing several stains, and using basic trigonometric functions, enables us to do a three dimensional recreation of the area of origin from which a blood-letting event occurred."

Kennedy goes on to point out that the disruption of a blood drop on impact with a surface is directly related to the texture of the surface. "A smooth surface, such as glass,
will provide the recording of a stain with clean edges and shapes of proper geometric proportion. A rough surface, like concrete, will break the surface tension irregularly and generate a star burst, or spinning effect. An experienced analyst is able to use some of the most disrupted stains to recreate the event. Arterial spurts, for example, when compared with the anatomical location of the injury may provide information about the position when the injury was inflicted and any subsequent movement by the injured party. Castoff patterns, or drops that are thrown off of a swinging instrument in the arc of the swing, can illustrate the position of the assailant when swinging a knife, or club."

Other crime scene analysts make the analysis of blood drops and spatters a bit more standard, but are aware, like Kennedy, that the surface type has a significant effect on just how the blood will appear. Distance estimates such as those provided in the following list are of little value unless the effects of a surface are known.

According to the basic teaching texts, the shape of a blood drop can reveal a lot about the conditions in which it fell. Given the many variations in what can happen at a crime scene, the experts don't necessarily all agree, but a flexible rule of thumb with a generally smooth and non-porous surface might be the following:

  1. If blood falls a short distance — around twelve inches — at a 45-degree angle, the marks tend to be circular
  2. If blood drops fall several feet straight down, the edges may become crenellated, and the farther the distance from the source to the surface, the more pronounced the crenellation
  3. A height of six feet or more can produce small spurts that radiate out from the main drop
  4. If there are many drops less than an eighth of an inch across, with no larger drop, then it may be concluded that the blood spatter probably resulted from an impact
  5. If the source was in motion when the blood leaked or spurted, or if the drops flew through the air and hit an angled surface, the drops generally look like stretched-out exclamation marks. The end of the stain that has the smallest size blob indicates the direction in which the source was moving.

It must be emphasized that blood pattern analysis is a complicated discipline and requires experience with many different situations to learn to do an accurate reading. While any of the above statements may be true, there can also be exceptions, and all interpretations are contingent on the factors that make up the context of the crime scene, most specifically the surface on which the blood made an impact.

"All classifications of bloodstain patterns help in the reconstruction of the events," Kennedy points out. "Spatter patterns give the nature of the force and positioning of the victim when shot or bludgeoned. Castoff patterns reveal the positioning and the possible size of the assailant. One also gets an indication of the size of the instrument swung and whether the swinger is left- or right-handed. Transfer patterns and hemorrhage or drip patterns give the direction of movement after blood is shed and can give an indication of timeframes. Arterial spurting can give the position, movement and seriousness of the injury, while 'shadows' — the absence of blood where one would expect to find it — suggest movement or removal of objects and changes to the scene."

A case in England in 1984 shows the importance of blood pattern analysis. A village womanizer named Graham Backhouse was found injured in his home with slashes across his face and chest. A neighbor with whom he'd had a dispute lay dead nearby, shot by Backhouse, who claimed the man had attacked him. However, the blood patterns showed that Backhouse had been standing still or moving slowly when he was wounded, rather than being in the sort of struggle he described. In that case, the blood would have been flung against surfaces to produce the elliptical pattern. Also, there was no blood from Backhouse on his gun or near the victim. The conclusion was that he shot his victim and then inflicted the wounds on himself. Along with other evidence, the blood analysis helped to convict him of murder.

"I have worked many cases in which bloodstain patterns contributed significantly to a guilty plea or guilty verdict," Kennedy recalls. "I have also worked cases in which the bloodstains did not support the initial allegations and the defendant was convicted of a lesser crime, or the charges were dismissed. For example in People vs. Brett Brooks Harris in Sacramento, the defendant claimed his stepfather had beaten his mother to death and then attacked him. Brett said he took the maddux handle from his stepfather and killed him in self-defense. Yet the bloodstain patterns showed that the stepfather was down and incapacitated before the mother, and both victims had been beaten more than they would have been during a single event. Based on bloodstain pattern analysis, Brett was held to answer from the preliminary hearing and, after serology validated the analysis, he pled guilty before trial."

In another case on which Kennedy worked, People vs. Pallermo in San Joaquin County, the defendant claimed the female victim had accidentally shot herself. "However, the bloodstain pattern analysis and computer models showed the defendant's rendition to have been an impossibility, and it placed the shooter across the room with the victim crawling into the corner to get away from the threat of the gun. The jury found the defendant guilty of second degree murder."

Royal Canadian Mounted Police unit
Royal Canadian Mounted Police unit

Asked about current research that may provide breakthroughs for forensic investigation, Kennedy said, "Bloodstain pattern analysis involves a constant need for research and development. The more cases that are worked and the more investigators involved, the more sophisticated the discipline will become. Probably the most advanced research has been done by members of the Crime Scene Bloodstain Section of the Royal Canadian Mount Police, Forensic Support Services. The RCMP is the only agency I know in the world that assigns and trains experienced crime scene investigators to do bloodstain pattern analysis only. They have developed a number of protocols that have been adopted around the world. Dr. Fred Carter, a professor of physics, has worked with the RCMP to develop several computer programs to teach the new analyst and help the experienced investigator."

No matter what kind of analysis is used on the blood at a crime scene, care must be taken to handle it properly and to prevent putrefaction. Photos and notes should be taken before any blood is lifted. Samples should not be exposed to heat, moisture, or bacterial contamination, because this shortens the survival time of proteins, enzymes, and antigens. Delays in getting samples to the lab must be avoided at all cost, because it can diminish evidential value.

This was one of the central issues in the most prominent case of the past decade in which blood analysis was a primary feature: the O. J. Simpson investigation.


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