What Does a Blood Spatter Analyst Do?

Bloodstain Pattern Analysis (BPA) is one of the specialty in forensic science. The analysis of blood splatter morphology utilizes physical science content such as biology, chemistry, and mathematics. Just following the relevant scientific procedures can produce strong evidence and make it an effective tool for scientific forensic staff.

Blood splatter analysis

Bloodstain pattern categories

How to divide and define the blood splatter mode can be based on the following three blood splatter formation modes: passive, projection, transfer or contact. Using this definition, the following glossary of IABPA recommendations from the International Association of Spill Morphology Analysis is available.

Blood droplets fly in the air from low, medium and high speed impact splashes. Different velocities represent how much energy is transferred into the blood droplets to produce different forms of blood stains.

Low Speed Impact Splash (LVIS)

In general, objects come in contact with the blood source at a speed of less than 1.5 meters per second. Blood splatter marks are generally larger than 3 mm in diameter.

Medium Velocity Impact Splash (MVIS)

During normal production, objects come into contact with the blood source at a speed of 1.5 m / s to 7.5 m / s. Blood splatter marks are generally 1 mm to 3 mm in diameter and can be produced by actions such as a knife.

High Speed Impact Splash (HVIS)

In general, the object comes into contact with the blood source at a speed of more than 30 meters per second. Blood splatter traces are generally smaller than 1 mm in diameter, and may even be misty, and can result from gunshots, explosions, high-speed machines, coughing, sneezing and arterial spraying.

Observing a drop of blood in the experiment will often form a sphere in flight instead of an artistic teardrop shape. This is due to the fact that the binding molecules of surface tension are brought together to form a state at the time of dropping.

When this blood cell splashes until it hits a surface to form a bloodstain, the direction of its splash can be determined from it to find the location of the blood source.

Sometimes a single splash of blood is not enough to determine the location of the blood source at the scene of the crime. Multiple bloodstain patterns should be calculated at the same time and a triangular trajectory should be calculated to determine its blood source area.

Determine the blood splatter angle

As mentioned earlier, the blood is dripped in a spherical shape. When contacting a surface, a good elliptical bloodstain is formed, so the examiner can calculate the direction of the bleeding source based on the length and angle of the long and short axis of the bloodstain.

To accurately measure and calculate, you need to go through complicated analysis procedures. Assurers generally use the following two methods:

"Cyclic observation of blood stains of 0.2 mm or more in diameter, using a scientific calculator or spreadsheet to calculate the relevant angles.

"Blood splat morphology analysis software Bloodstain pattern analysis (bisphenol) software uses elliptical pixels to overlay the bloodstain image to calculate the relevant angles. Software analysis can produce very accurate and repeatable results.

photography

Crime scene photography has its unique requirements. When a crime scene involves a bloodshed, special attention must be paid to the requirements of bloodstains to record the scene. The current methods include: 35mm photography (black and white, color and special film), digital cameras, video tapes (HI8, DV, etc.). Each approach has its pros and cons.

Types of crime scene photos:

"The overall wide-angle image (28-35mm lens) for shooting the scene can provide the overall layout of the scene without anyone present.

"Intermediate shooting-use a 45-55MM lens to shoot a more detailed overall layout, including a single blood splash pattern.

"Close-up shootinguse a macro lens to capture every detail. For example, a blood splatter pattern caused by a medium-speed impact can contain thousands of tiny blood spots to be analyzed, some of which need to be analyzed separately. Image.

Note: Projection of blood