1. Expert Profile
Matthew Steiner is a first-grade detective with the New York City police department’s crime scene unit. He is a twenty-three-year veteran with over eighteen years of experience as a crime scene investigator. He is the lead instructor for the crime scene unit. Detective Steiner has investigated over 2000 crime scenes. He has been deemed an expert witness in latent prints, crime scene investigation, bloodstain pattern analysis, shooting reconstruction, and crime scene reconstruction in New York City, state, and federal courts.
2. Foreground
Investigators can derive a lot of information from the bloodstain patterns at a crime scene which includes the origin, type of instrument that caused the bloodstains, the direction and relative positions of the victim, assailant and suspects, locations and movement of victim and assailant during the attack, number of blows or gunshots, and the truthfulness of any witnesses. Three major questions raised are –
- How did it get where it was?
3. Analyzing Bloodstains
Steiner shared his experience in BPA by showing us his video on the YouTube channel WIRED where he beautifully demonstrates every type of blood drip pattern, flow patterns, pooling of the blood or saturation, spatter patterns, and the various forces acting on the shape of the drops
3.1 Shape of a Blood Drop
A blood drop consists of the main drop and its company drops or satellite drops. Typically, a drop when breaks away from its larger source remain spherical because of surface tension, unlike the typical media representation of a “teardrop” shape, until it strikes a surface without breaking into droplets in the air during the flight/fall.
The shape of the blood drops falling on different surfaces is different. Plexiglass surfaces will exhibit a smooth outline of the blood drop whereas wooden surfaces would result in a spiny outline as the surface itself disrupts the blood drop’s surface tension.
Citing the case history of O. J. Simpson murder trials Steiner explained the various types of patterns of bloodstains and the potential loss of crucial evidence during the crime scene processing and investigation.
3.2 Types of Patterns
Types of patterns that are found at crime scenes are passive, spatter, transfer, and altered.
- Passive Patterns resulting from a swiping movement are termed as feathering. Saturation results when an object absorbs the blood like a mattress or pillow. Blood pools are formed when it accumulates downhill. Blood flow can be defined as the change in shape and direction of a bloodstain due to the influence of gravity or movement.
- Spatter Patterns are created when a force is applied to a liquid blood source. Spatters can be forward or backward. The direction of impact can be determined by a telltale clue i.e., the tail of the drop falling on the surface. The angle of impact, θ, the stains hit the surface is calculated by measuring the length of the stain and it is divided into the width of the stain and the arcsin(x) of that value will give us the angle of impact. It can be mathematically represented using the Balthazard formula –
arcsin〖[(width of the stain in mm)/(length of the stain in mm)]=angle of impact〗
When θ = 90°, the drop is a circle.
Projection Spatters can be produced by several different mechanisms, including stabbings, beatings, gunshots, arterial bleeding or spurting, cast-off (flying motion of drops), splashing, and expiated blood (blood sprayed out of the mouth or nose from airways while exhalation).
- Transfer Patterns result when an object soaked with blood comes in contact with an unstained object. Bloody fingerprints and shoeprints fall into this category. Blood-soaked fabric can leave behind a recognizable pattern. Investigators may be able to use it to determine what type of clothing the attacker wore.
- Altered Patterns are those whose appearance indicates the blood and/or pattern has undergone physical and/or physiological alterations. Blood dries from outside to inside.
Following types of altered patterns are usually seen in crime scenes:
- Voids are the absence of stains in an otherwise continuous bloodstain pattern.
- Diluted bloodstains can be due to rain or snow or a deliberate attempt to clear up a scene.
- Fly spots result from flies present at the scene which feed on the blood found there. This blood is tracked about, regurgitated, and excreted by flies.
- Wipe patterns are altered bloodstains resulting from an object moving through pre-existing wet bloodstains. The edges of a stain will dry to the surface, producing a phenomenon called skeletonization. This usually occurs within 50 seconds of deposition for drops, and it takes longer for larger volumes of blood. If the central area of the pooled bloodstain is then altered by wiping, the skeletonized perimeter will be left intact. This can be used to interpret whether movement or activity occurred shortly after the pool was deposited or later after the perimeter had time to skeletonize first. This may be important for classifying the source of the original stain.
- The feathering effect results due to the wiping motion on the bloodstain on a surface, which further helps us interpret direction and movement at a crime scene. Such marks are usually indicative of drag marks where the victim is bleeding whilst their body is moved from the scene, or when a suspect runs their hands on a surface like a wall.
4. Methodology for BPA
- Become familiar with the scene.
- ID and categorize discreet patterns
- Evaluate directionality and motion
- Evaluate angles of impact, convergence point, and origin
- Asses relationships of patterns and evidence
4.1 Area of Convergence
Intersections are generated by lines drawn through the long axes of individual stains that indicate in two dimensions the locations of the blood sources. Bloodstain pattern analysis possesses a subjective nature in the calculation of area of origin and has inherently faced criticism in the scientific community. Current software used in analyzing the area of origin (AO) for medium velocity spatters doesn’t account for alterations during the formation of the stains across different targets.
4.1.1 FaroZone 3D – Blood Spatter
FaroZone 3D is the first of its kind to enable the investigator to move fluidly between 2D and 3D spaces and enhance incident reconstruction quality analysis, pre-incident plans, and courtroom presentations.
4.1.2 Point of Convergence
A two-dimensional representation of the point where lines tracking the pathways of two or more spatters meet, indicating a general location of the blood source relative to the spatters.
4.1.3 Point of Origin
A three-dimensional representation of the point where lines tracking not only the pathways but also the angles of impact of two or more spatters meet, indicating the general spatial location of the blood source. The point or area of origin is calculated using the right triangle method. If we know the angle of impact, θ, and the distance from the stain to the area of convergence, x, we can figure out the area or the point of origin in 3-D space. The hypotenuse of the right triangle is calculated by the tangent using sohcahtoa
tanθ⋅x=(distance of the point of convergence)
4.2 Chemicals to Detect Latent Bloodstain
- Leuco-Crystal Violet is a dye that is used as a general protein stain. General protein stains are less specific than presumptive blood testing reagents. However, the reduced form, LCV, is a presumptive blood reagent. The colorless LCV turns purple on contact with latent blood. It can be used in available light and is very effective on light-colored surfaces.
- Bluestar is easy to mix in the field. Its reaction with blood can be observed readily without having to create complete darkness. Bluestar test is extremely sensitive—capable of detecting bloodstains diluted to as little as 1 in 100,000. For this reason, spraying large areas such as carpets, walls, flooring, or the interior of a vehicle may reveal blood traces or patterns that would have gone unnoticed under normal lighting conditions. It is important to note that Bluestar does not interfere with any subsequent DNA testing.
5. Cautions to BPA
- Alternate explanations are possible
- Not usually smoking gun evidence
- Don’t overreach. What you can’t prove you can’t say
6. Conclusion
Bloodstain pattern analysis provides a clear-cut understanding of the sequence of events that may have occurred while the execution of a criminal act. While in the field, it's better to do all these methods discussed above. Establishing relationships requires observations and interpreting them correctly.
7. Personal Note
The whole session was more than just a lecture, it could be deemed a mini-workshop on interpreting bloodstain patterns focusing on practical stuff more than theoretical aspects. It was much interactive and probably the coolest lecture I attended on any platform.