Tag Archives: blood

Bloodstain Patterns on Textile Surfaces: A Fundamental Analysis

Bloodstains on fabric

Bloodstains on fabric

Article authored by: Stephen Michielsen, Michael Taylor, Namrata Parekh, Feng Ji

Abstract

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

Serological Evidence in Sexual Assault Investigations

By Robert R.J. Grispino, M.A.
Special Agent Serology Unit, Laboratory Division FBI Headquarters

This Article Originally Appeared in the FBI Law Enforcement Bulletin, October 1990.

NOTE: The following article presents a purely scientific approach to sexual assault evidence collection. The scientific step-by-step procedures that are explained here should always be accompanied by supportive treatment of the victim. It should also be noted that the investigating officer will be responsible for both overseeing the execution of the medical procedures described and managing the collection of the physical evidence.

Police officers throughout the United States routinely handle and oversee sexual assault investigations. Yet, these officers rarely receive training on the proper methods to be used for sexual assault evidence collection and preservation. As a result, valuable physical evidence may either be overlooked or inadvertently allowed to deteriorate biologically. This article establishes proper evidence collection and preservation protocol in sexual assault matters and demonstrates how modern forensic serology can aid in the eventual successful prosecution of the assailant. Continue reading