There is no question that the presentation of bloodstain pattern analysis is a powerful piece of evidence at a trial. The graphic images of bloodstain at the crime scene and the detailed analysis of how those stains arose paint a compelling picture of the events that took place as the crime unfolded. The prosecutor's presentation and the testimony of the individual who analyzed the bloodstain patterns can go a long way towards sealing a conviction of the perpetrator on trial.
Bloodstain patterns present a complex form of evidence and require detailed analysis in order to reach accurate conclusions as to what events actually took place. While some crime scenes may be relatively simple to interpret others are much more complex and require very detailed analysis. Accurate bloodstain pattern analysis requires a well trained and experienced examiner. However, in some cases an analysis is made and conclusions drawn by individuals with inadequate training or no formal training at all. In some instances where a high-profile crime is putting pressure on finding a prime suspect, the bloodstain analysis may be incomplete, or because of time delays important aspects of the complex pattern may be analyzed improperly or not at all.
In cases where a victim may still be alive, bloodstain evidence can be compromised by emergency medical personnel moving the victim or furniture, thus changing the scene as it actually occurred. It can also be alerted or damaged by law enforcement officers arriving first on the scene and rushing to secure the scene. Both of these situations could lead to a misinterpretation of some aspect of the overall crime scene.
Evidence is where you find it
Bloodstain evidence can occur upon any surface. While this is generally thought of as walls, ceilings, floors, tables, etc. important bloodstain evidence also occurs on the perpetrator's clothing or shoes. Once an individual is a suspect, if an immediate attempt to collect these items is not made these important pieces of evidence may be lost. The victim him- or herself may be an important source of bloodstain data. All too often, when the medical examiner's office receives the body, it is thoroughly washed down before the autopsy and vital bloodstain information may be lost. In some cases a bloody fingerprint of the perpetrator may be found on the body, and often is not apparent unless very rigorous examination of the body is performed.
The body may also provide evidence of the perpetrator's blood if they injure themselves in commission of the crime. In this case, blood drops on the victim or their clothes can provide evidence of passive drip or bloodstain from the perpetrator to the victim.
Even the simplest appearing crime scene represents a complex picture when there is significant bloodstain spatter present. Proper documentation of the scene is critical to allow a complete and accurate analysis of what transpired at the scene. In the case of a beating or stabbing, the victim may have moved one or more times in an attempt to escape the attack. Thus, blood evidence may occur within several rooms or hallways at a scene. If the victim moved within the same room, bloodstains may occur on the same wall but have arrived there at different times within the period of the crime. Cast-off blood patterns may occur at different angles and overlay one another, adding to the complexity of the analysis and increasing the chances for a misinterpretation of the results.
Photographic documentation of the entire scene is critical to preserve the scene as it was when originally discovered. Documentation of the bloodstain evidence requires that photographic images of the entire scene in all directions are taken. Bloodstain evidence begins at a point furthermost from the victim where the first bloodstain evidence is found. Significant areas of spatter need to be adequately photographed along this route. It is critical that the perspective of each photograph in relation to the entire scene is documented and preserved. All photos, overall, midrange or close-ups should include a standard reference scale such as the ABFO scale. If spatter is magnified, then the degree of magnification must be documented and verified with an appropriate scale of reference. If appropriate video equipment is available, then a video of the scene can also provide valuable information when the analyst is evaluating data at a later date.
While overall pictures of the crime scene are usually taken with a wide angle lens, mid-range pictures are taken with normal lens settings. These pictures give greater detail than the overall shots. A mid-range image could capture a single bloodstain pattern and allow all patterns to undergo more rigorous analysis back at the forensic laboratory.
A major area where inexperienced investigators or those not fully trained in bloodstain pattern analysis can make a significant mistake in interpretation of the scene is reliance too much on the mid-range images. Each image will provide a set of data, but unless these data are interpreted with regard to the whole scene, an inadequate or in some cases wrong interpretation of the bloodstain evidence can occur. According to Detective Lieutenant Kenneth Martin of the Massachusetts State Police Crime Scene Services Section, investigators often "neglect to look at the entire pattern and usually focus on [only] a portion of the pattern." Since bloodstain analysis is so crucial to many trials, it is important not to make a mistake by focusing only on the mid-range evidence.
Training in bloodstain pattern analysis is available thru the International Association of Bloodstain Pattern Analysts (IABPA), which sponsors many training sessions annually, ranging over virtually every aspect of bloodstain pattern analysis, including photography and video documentation. These training classes and workshops are held at various locations around the country. CSI technicians and investigators that specialize in bloodstain analysis should have a minimum of a 40 hour of training, including lectures on theory and actual hands on spatter pattern analysis. The International Association for Identification (IAI) has a Bloodstain Pattern Analyst Certification program. Training classes are also available from groups such as the National Association of Medical Examiners.
Doug Hanson, Ph.D. is a Ph.D. Biochemist who has operated toxicology and analytical chemistry laboratories for over 25 years. He is also a freelance writer who has written extensively for law enforcement, EMS and first responder magazines. His areas of expertise and written articles include: forensic investigation, DNA analysis, blood spatter, trace analysis, toxicology, drug and analytical chemistry, and forensic anthropology among others. He has written about car bombs, IEDs, soft targets, biological and chemical agents and attack scenarios. He has written on juvenile arson and illegal meth labs. Doug has written and published a book entitled The Eider Files, a novel about bioterrorism.