10.1: Introduction

The topic of bloodstain pattern analysis is best left to the many competent training programs available on the forensic training market, and to textbooks dedicated to bloodstain pattern analysis such as Tom Bevel and Ross Gardner’s Bloodstain Pattern Analysis, 3rd edition, CRC Press or Toby Wolson’s Handbook or Bloodstain Pattern Analysis, 1st edition, CRC Press. However, your author does believe the reader should have the ability to recognize bloodstain patterns within a crime scene, and to understand the potential significance of bloodstain patterns to the successful investigation of a violent blood-letting event or crime. Therefore, the purpose of this chapter is to familiarize the reader with an understanding of the proper discovery, recognition, preservation, documentation, and collection of specimens, the result of a blood-letting event, but not necessarily the ability to perform bloodstain pattern interpretation or analysis. For contemporary bloodstain pattern terminology, please refer to the American Academy of Forensic Science (AAFS) AAFS Standards Board (ABS) Technical Report 033, June 2017 (www.aafs.org/sites/default/files/media/documents/033_TR_e1_2017.pdf). The full list of terminology will be found at the end of this chapter.

It is essential that major blood-letting events must be properly mapped, diagrammed, and photographed. Contrary to the beliefs of some defense attorneys, a bloodstain pattern analyst can effectively analyze a blood-letting event using photographs taken at the scene; provided the photographs include overall measurements, the predominant stains are represented with a scale, and that the means to determine that the camera was perpendicular and parallel to the target is present. Documenting the crime scene for bloodstains is time consuming and requires the technician to develop a “mapping” plan, and to be meticulous about documenting and measuring the stains. Thus, the technician will need to have at least the rudimentary understanding of the characteristics of blood in flight. For that, it is important for the technician to understand that blood is a non-Newtonian viscoelastic fluid. Unlike water, which is held together by surface tension, blood is cohesive and is therefore held together by viscosity and internal cohesion. Therefore, blood is harder to break apart when energy is applied. Because of this, blood maintains a spherical shape in flight. It is because of this round shape that we can make an analytical examination of the resultant stains once the blood has impacted a surface. We can apply the laws of physics and mathematics to the observable characteristics of these patterns to determine the nature of the force that produced the patterns, the number of blows struck, the type of force applied, the sequence of events, the angle of impact and origin of the blood-letting source, and the position of the participants. The technician must also understand that a distribution of bloodstains on a target is called spatter patterns. This is of emphatic insistence with bloodstain pattern analysts and is beyond debate. The word “splatter” is a portmanteau word (a word created by blending the sounds of two words that have a similar meaning) created by combining the words “splash” and “spatter.” Although our terminology includes a splash bloodstain pattern, which is produced when a large volume of blood spills onto a surface, the majority of bloodstain patterns are not the result of a splash. Therefore, it would be incorrect to generalize all bloodstain patterns with a word that includes “splash.”

Figure \(\PageIndex{1}\): A falling drop of blood and the same drop enlarged. Note the spherical shape. It is because of this shape that bloodstain pattern analysis is possible. – Author’s collection

The technician will need a camera mounted on a tripod and must be cognizant of the need to augment or control lighting. The photographs need to be sharp and in focus. It is also essential that the analyst know that the stains being photographed are indeed bloodstains. Therefore, the technician must conduct presumptive testing of the predominant stains using a product like phenolphthalein or leucomalachite green, and ideally the Bluestar OBTI Immunochromatographic Rapid Test™ to determine species, and, following documentation, to collect specimen and control swabs for DNA analysis. The surface upon which the blood has landed is referred to as the target.

The technician should assess the crime scene and assign each target, the area where the blood impacted, with an individual alphabetical or numeric designation. Each pattern within the designated target will then be given a sub-designation. Therefore, if the technician assigns one target area, such as the north wall in a cell, with the capital letter ‘A’ then the patterns within that area will have a numeric sub-designation, such as pattern 1, and a predominant stain can be selected from this pattern and documented. If the technician decides to document more than one stain in the pattern, each of the individual stains is then represented by a small letter. Therefore, a cast-off impression on the north wall will be designated as target ‘A,’ pattern 1 and stain ‘a’ (A1a), ‘b’ (A1b) and so forth.

It is necessary to include full-length measuring tapes vertically and horizontally in the mapping photographs. Although your author does have a few 48” yellow construction bubble sticks that work great in the crime scene, there is nothing that beats Evident Crime Scene Products’ 48” SuperSticks™ for bloodstain mapping and Sirchie’s SEARCH™ or Pocket Rod ™ tape measure used with the metal base that allows the tape to stand by itself. Both products are reasonably priced and an essential tool in the crime scene kit. Larger areas may require the use of fiberglass tape measures for horizontal measurements. Your author keeps a drawer full of disposable soft sewing tape measures. They are reasonably inexpensive and can be discarded after use to prevent contamination. Be certain to have strong adhesive tape on hand to keep the tape measures on the wall for the photographs.

The technician will also need alphabetical and numerical adhesive-backed stickers, adhesive-backed scales, and adhesive-backed circles. Although many of these products are available at all the forensic supply retailers, as well as craft and hardware stores.

Figure \(\PageIndex{2}\): Impact pattern bloodstains on the exterior of a vehicle. Note the use of the orange dot underneath the capital letter to indicate the plane of the camera. – Author’s collection

Figure \(\PageIndex{3}\): Copy and Paste Caption here. (Copyright; author via source)Figs. 10.2A/B – Impact pattern bloodstains on the exterior of a vehicle. Note the use of the orange dot underneath the capital letter to indicate the plane of the camera. – Author’s collection

Figure \(\PageIndex{4}\): A large area with multiple blood-letting events recorded. Note the discarded latex gloves carelessly contributed to the crime scene by responding medical personnel. – Author’s collection

Figure \(\PageIndex{5}\): “Mapped” bloodstain patterns on a cell door. It is always a good idea to put something behind the door so that it does not open as you are taking the photograph. – Author’s collection

Figure \(\PageIndex{6}\): Examples of different mapping techniques. – Author’s collection