Blood spatter analysis
Blood spatter analysis (Forensic Science)
Blood spatter analysis is a valuable tool of forensic investigators in the determination of the events that transpired during crimes in which victims received wounds that resulted in bloodstains. Investigators can apply the physical principles of the motion of blood through the air to the patterns of blood droplets found at crime scenes, as well as the droplets’ overall shapes, to ascertain the exact locations where victims’ wounds were received.
(The entire section is 70 words.)
Blood Spatter Ballistics (Forensic Science)
Blood is a fluid of constant density that is not affected by temperature, pressure, or other atmospheric conditions when it is in flight. The large surface tension of blood drops holds them together during their time of flight, and as they move through the air, the drops assume a spherical shape. Blood spatter patterns are influenced by the distance the blood travels through the air and the material with which it comes in contact.
A blood drop that falls straight down from its ejection point will project a circular stain on the material that absorbs it. In contrast, a blood drop that travels an extended distance from the source of the wound will follow a parabolic path, striking any surface it meets at an angle. When this angle of impact is not 90 degrees measured with respect to the horizontal surface (which would be a straight-down motion), the blood drop will leave an elongated (elliptical-shape) stain on the surface that it strikes. The more pointed end of the stain will be in the direction the blood drop was traveling.
(The entire section is 178 words.)
Analysis of Blood Spatter (Forensic Science)
The patterns of bloodstains observed on surfaces provide evidence of the points of impact of wounds and the force of the punctures. crime scene investigators can use the directionality of bloodstain patterns to work backward toward the two-dimensional point on the surface level with the blood spatter to identify the point of ejection and distance from the wound. (Given that the pointed ends of blood drops indicate the direction of travel, the more rounded ends converge toward the point of origin.) In the early days of blood spatter analysis, crime scene investigators laid out series of strings or wooden rods in the diverging direction of a blood spatter pattern to determine the convergent point. Modern forensic tools include computer software packages that use the data of the coordinates of blood spatter to determine the point of emergence of the blood drops.
In addition to the two-dimensional determination of the victim’s position when the injury occurred, the blood spatter analyst can estimate the vertical position of the wound from the angle of impact of the blood spatter. This can provide evidence in terms of whether the victim was standing, sitting, or lying down at the time of the injury. In examining a bloodstain, a forensic investigator measures its length and width. The angle of impact is then determined by the trigonometric relation involving the sine of the angle: Sin(a) =...
(The entire section is 444 words.)
Obstacles to Useful Analysis (Forensic Science)
The major problem faced by forensic scientists attempting to conduct blood spatter analysis is that many crime scenes lack well-defined blood spatter patterns even when blood is present. Difficulties may arise because of the effects of blood on different surfaces, because smaller blood droplets have broken off from larger droplets, because the victim moved after the injury and disturbed the initial spatter pattern, or simply because of the overall chaos of an environment where a violent crime has been committed. In such cases, often the only substantive evidence that can be gained from bloodstains involves identification of victims and possibly assailants through the blood types found at the crime scene and through analysis of DNA (deoxyribonucleic acid) extracted from the blood found.
(The entire section is 122 words.)
Further Reading (Forensic Science)
Adams, Thomas F., Alan G. Caddell, and Jeffery L. Krutsinger. Crime Scene Investigation. 2d ed. Upper Saddle River, N.J.: Prentice Hall, 2004. Handbook for law-enforcement professionals includes a chapter titled “Evidence Collection” that has an informative section on blood and blood analysis.
Bennett, Wayne W., and Kären M. Hess. Criminal Investigation. 8th ed. Belmont, Calif.: Wadsworth/Thomson Learning, 2007. Comprehensive textbook provides in-depth discussion of forensic techniques and procedures. Includes checklists and questions at the ends of chapters to highlight the most important ideas presented.
Camenson, Blythe. Opportunities in Forensic Science Careers. Chicago: VGM Career Books, 2001. Presents accounts of professionals working in forensic science and identifies the education needed and the job responsibilities related to various disciplines within forensics.
James, Stuart H., and Jon J. Nordby, eds. Forensic Science: An Introduction to Scientific and Investigative Techniques. 2d ed. Boca Raton, Fla.: CRC Press, 2005. Comprehensive introductory textbook uses many case studies to illustrate crime investigation methodologies. Includes a section on recognition of bloodstain patterns.
Nickell, Joe, and John F. Fischer. Crime Science: Methods of Forensic Detection. Lexington: University Press of Kentucky, 1999. Very thorough examination of forensic...
(The entire section is 193 words.)