Bloodstains on fabric
Article authored by: Stephen Michielsen, Michael Taylor, Namrata Parekh, Feng Ji
Bloodstain pattern analysis, BPA, on hard surfaces (such as walls, tables, appliances, hardwood floors, etc.) has grown into a science-based investigative tool that can help determine scenarios that are consistent with or counter to the events described by witnesses or suspects. At the vast majority of crime scenes involving a bloodletting event, textiles are present as apparel, household textiles (sheets, towels), upholstery, carpets, and so forth. Yet, the science of BPA is not able to render the same level of confidence in the analysis as on hard surfaces due to the complex structure of textiles and their ability to wick liquids. In the work described herein, a detailed examination of factors that affect BPA on two textile fabrics, an unbalanced 130 x 70 plain woven 100% cotton bed sheeting fabric (often referred to as a 200 thread count bed sheet) and a 100% cotton jersey knit T-shirt fabric.
During this study, both porcine blood and several synthetic blood recipes were used. The dynamic impact tests (time after impact < 100 ms) used porcine blood, while most wetting and wicking experiments employed synthetic blood (time after impact > 100 ms). Most of the synthetic blood recipes examined performed badly. Either they would not dry or they did not wick into the fabrics, but remained on the surface. A synthetic blood recipe from the American Society for Testing Material (ASTM test method F1819-07) performed well, but its viscosity and surface tension were both lower than typical human blood. Thus, this recipe was modified to lie within the range of surface tension and viscosity of human blood. It was used for the majority of wicking and wetting experiments. In a preliminary comparison, it was found that synthetic blood SB5 behaved similarly to porcine blood in many aspects, but the SB5 stains were significantly larger than the porcine bloodstains. We attributed this difference to the presence of red blood cells, which behave as particles, as well as plasma, which behaves as a liquid, in porcine blood. SB5 is an aqueous solution and behaves entirely as a liquid. Continue reading
By Kathy Steck-Flynn
A man is found dead in an abandoned house. Upon examination the medical examiner finds that the man was killed by a single gunshot to the head. Three local teens where observed near the house two days earlier. They are picked up and questioned by police. When pressured, the teens admit to having stolen one of the boys’ father’s guns. They had taken turns shooting at the windows of an abandoned house.
The teens admit that John shot the gun first, then Jay and last was Fred. At the scene the investigators find three bullet holes in a window. They analyze the angle of each bullet hole in relation to the victim and find that the bullet which passed through the far right side of the window pane is the one which fatally wounded the man. Continue reading
by D.H. Garrison, Jr.
Originally published in the Association of Firearm Toolmark Examiners Journal, Oct. 1993.
Just because a shot was fired, and just because someone was injured or died as a result of the shooting, and just because a shooting reconstruction was completed…this does not mean that the expert can render an opinion about the intent behind the bullet thus fired.
While many an attorney, whether prosecution or defense, wants to “prove” the intent or lack thereof to a jury, and sometimes tries to use a expert witness to accomplish that end, this does not mean that the shooting reconstruction expert has any scientific basis whatsoever to state an opinion as to what was or was not the intention of the shooter at the moment of the shooting. Intent, after all, is usually an “ultimate issue” and, thus, the purview of the jury, the finders of fact, and cannot properly be addressed by the expert. Continue reading
by Daryl W. Clemens
This article originally appeared in the MAFS newsletter, 27(2), April 1998.
Crime Scene Reconstruction- The use of scientific methods, physical evidence, deductive reasoning and their interrelationships to gain explicit knowledge of the series of events that surround the commission of a crime.
-Association for Crime Scene Reconstruction, The Scene, 4(1), Jan 1997, p. 2.
Criminal Profiling- The application of psychological theory to the analysis and reconstruction of the forensic evidence that relates to an offender’s crime scenes, victims and behaviors.
– Turvey, B., “CP101: An Introduction to Criminal Profiling”, Online Course,
http://www.corpus-delicti.com, May 1997.
While both of these activities may appear to be similar and are in fact related, it is important to note that they are not the same. The difference between the two is most easily understood by looking at which questions about the crime they attempt to answer.1,2,3,4 Crime Scene Reconstruction looks at the physical evidence and attempts to determine “What happened?” and “How did it happen?”.5,6 Criminal Profiling looks at the physical evidence and the reconstruction and attempts to determine “Why may this have happened?” and “What does that tell us about Who may have done it?”.7 It is important to keep in mind that only those directly involved in the crime know for sure what happened and why, and they may be unable or unwilling to say. 8,9
By Dean H. Garrison, Jr.
This article originally appeared in the MAFS newsletter April 1996.
“I tend not to try to determine why people do things at crime scenes.”
-Criminalist Charles Morton
California v Menedez II, Trial transcript 12-5-95
Crime scene reconstruction may answer the question of where a victim was standing when an axe hit him or who stepped in the pool of blood by the door or what caused the revolver’s hammer to fall or when the third shot hit the car window or how the knife ended up out on the patio, but the crime scene reconstructionist cannot answer the ultimate question, the final question that tugs at everyone’s mind, the all-encompassing, all-seeing, all-knowing question of WHY did the crime happen? This may account for the fact that attorneys (for either side) very seldom ask “Why?” questions. Continue reading
by D. H. Garrison, Jr.
Forensic Services Unit
Grand Rapids Police Department
Grand Rapids, Michigan
This Article Originally Appeared in the MAFS Newsletter, October 1991.
Forensic science is the product of an uneasy and unholy mating of Science,
the objective seeker of truth and knowledge, and Forensics, the argumentative
persuader of courtroom advocacy. It is not called Justice Science, Law Science,
or Truth Science, as many of us would like to imagine. We are a bastard child,
an orphan, but still the subject of an intense child custody battle between
our estranged parents, the truth seeker and the advocate. The tug-of-war
goes on daily for our loyalties and confidences, each side offering candy
and warm hugs. These separated parents have visitation rights. Sometimes
they take our brothers and sisters away. Sometimes they don’t come back. Continue reading