Introduction to Bloodstain Pattern Analysis | Matthew Steiner

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 – 

• Who shed the blood?

• How did it get where it was?

• What was the sequence?  

3. Analyzing Bloodstains

Steiner shares 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. 

• 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 – impact spatters 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.