What does area of convergence tell investigators?

If you have a number of bloodstains, the area of convergence can be determined by drawing lines from the leading edge of stains through the long axis.

Table of Contents Show

What is the area of convergence and how does it help an investigator?
What does area of origin tell investigators?
What does the area of convergence reveal?
Why is the area of convergence used?

The lines come together in a general area where the blood has emerged, helping to locate the origin of the bloodstains.

You can view the process on the tablet on the right side or use this link for a description of the animation.

Bloodstain Pattern Analysis is the study of the size, shape and location of bloodstains, in order to provide an interpretation of the physical events which gave rise to their origin.

IFS experts have investigated hundreds of cases where bloodstains tell the story. Our knowledge is extensive and we perform our own tests to reproduce events.
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When force (an impact) is applied on a source of liquid blood, an impact pattern is created around this event.
The ‘angle of impact’ is the acute angle formed between the direction of a blood drop and the plane of the surface it strikes. After the impact the resulting blood droplets move through the air like a sphere. If a drop of blood hits a surface at an angle, it creates an ellipse. The formula for determining the angle when the blood drop hits the surface (‘impact angle’) is shown. The arrow shows the direction in which the blood drop went before it hit the surface.

On the following photos an impact pattern is shown that has been created with a hammer. The source of liquid blood at the time of impact was located on the wood block. Variation in size and shape of the blood spatter is clearly visible. The location where the blood spatter is more or less round shaped gives an indication of the height where the impact on the blood source has taken place.

In the figure shown here the area of convergence is determined by drawing lines on a two dimensional surface through the axis of the blood spatter. The area where the lines intersect, is most likely the location where an impact in blood has taken place. An area of convergence from a murder case where a victim was murdered on a couch is shown here. The area inside the red circle on the wall, where the lines intersect, is the approximate height at which an impact in blood of the victim took place. The green line represents the top of the couch.

The individual courses of the blood spatter are lined out in the photo below. Using the formula above the angle under which the drops of blood hit the wall is determined. The victim was lying on a sofa at the time he was struck on the head several times with a bottle. The green line represents the top of the bench on which the victim was lying. The area of origin is where the pink lines intersect, indicated inside the red square. Within this area in the three dimensional space, the impact in blood of the victim most likely occurred.

Blood spatter that could form during a shooting incident
When a person is shot, for example in the head, two kinds of typical blood spatter patterns can be formed. Due to the high speed of the bullet and the damage that is caused in the wound channel, “back spatter” and “forward spatter” can be created. Back spatter is blood directed towards the source of energy or force that caused the spatter. Due to the high speed and the power of the bullet, the blood spatter that is created is usually less than 2 millimeters. Sometimes the force that is carried out on the blood is so great, that a misting pattern is formed. The blood appears to be as if it was sprayed.
With back spatter, tiny blood droplets are projected in the direction of the shooter. With forward spatter, small drops of blood travel along with the bullet through the opening where the bullet leaves the body. The patterns of forward spatter usually contain more blood and cover a larger surface compared to the pattern of back spatter, see the figure.

On the photos below patterns of back spatter and forward spatter are visible. These patterns were formed during an experiment. A shot was fired at a bloodied sponge that was put between two sheets of paper.

Patterns of projected blood (cast-off)
Patterns of projected blood form when an object, such as a knife, containing enough blood is swayed in the air. When stabbing through clothing often very limited amounts of blood are transferred on the stabbing object. This is caused, amongst other things, because the blood on the knife is kind of swept clean when the knife is pulled out of the clothes. A cast-off pattern is a bloodstain pattern created when blood is released or thrown from a blood-bearing object in motion. On photo 11 a pattern of projected blood is shown, caused by adding liquid blood to the fingers of a hand that is swayed through the air along a wall. A typical pattern of blood spatters that are in one line occurs.

Arterial spurting
An arterial spurting (or gushing) pattern is a bloodstain pattern(s) resulting from blood exiting the body under pressure from a breached artery. On the photo below a pattern is shown that was made on a wall in a lab using a big syringe.

Transfer patterns
A transfer pattern is a pattern that forms when a wet, bloody surface comes in contact with a second surface. A recognizable image of all or part of the object that caused the pattern can sometimes be observed in the pattern.
On the photos transfer patterns are shown that are caused by a bloodied hand and a bloodied shoe sole.

Wipe and Swipe pattern
A swipe pattern is the transfer of blood from a moving source onto an unstained surface. Direction of travel may be determined by the feathered edge. The photo shows a pattern where a victim was dragged by the perpetrator.

A wipe pattern is a bloodstain pattern created when an object moves through an existing stain, removing and/or altering its appearance. On the photo a wipe pattern is shown where a person on his socks walked through wet bloodstains.

Spill pattern
A spill pattern is a volume of blood that has fallen at once onto a surface.

Passive drops
Passive drops are drops of blood that are formed under the influence of only gravity. This is often observed in incidents involving moving injured persons.

Pool pattern
A pool pattern forms when blood has flowed in one place for some time, such as when a bleeding victim stayed there for a period of time.

Flow pattern
A flow pattern is a change in the shape and direction of liquid blood under the influence of gravity, pressure and/or movement of the object.Within the black and the blue circle, flow patterns are visible on the body of a deceased victim. Based on these patterns it can be said that the victim has been in two different positions while blood flowed over the body.

Void
A void is the absence of stains in an otherwise continuous bloodstain pattern. Photo 21 shows the location in the blue circle where a deceased victim bled severely before he died, leaving a void in the blood pool.

Luminol investigation
Luminol is a chemical that luminescence’s in the presence of blood with a bluish light. The first photo is taken before the room was treated with Luminol. With the naked eye traces of blood were barely visible. Due to the high sensitivity of the chemical reaction Luminol is very suitable to show remnants of blood, which are no longer visible to the naked eye (for example by cleaning. Luminol also reacts with substances other than blood, such as chlorine, metals and certain substances in some paints. False positive reactions may be excluded using a more blood specific test, like the tetra base test.
Interpretation of bloodstain patterns and latent traces of blood which are found using luminol, should preferably be carried out by a trained bloodstain pattern analyst.

With the interpretation of results of a Luminol investigation caution should be exercised. When a small amount of blood is cleaned with water, Luminol can create an image, where it seems like a much more blood has flowed. Because of the sensitivity of Luminol small quantities of washed away blood can cause strong luminescence. This luminescence tells us little about the amount of blood that is lost by a person.

What is the area of convergence and how does it help an investigator?

Area of convergence- The area on a two-dimensional plan where lines traced through the long axis of several individual bloodstains meet; this approximates the two-dimensional place from which the bloodstains were projected.

What does area of origin tell investigators?

Area of Origin -‐ The three-‐dimensional location from which blood spatter originated. Backspatter Pattern -‐ A bloodstain pattern resulting from blood drops that traveled in the opposite direction of the external force applied; associated with an entrance wound created by a projectile.

What does the area of convergence reveal?

Area of Convergence - The area containing the intersections generated by lines drawn through the long axes of individual stains that indicates in two dimensions the location of the blood source.

Why is the area of convergence used?

Area of Convergence. If you have a number of bloodstains, the area of convergence can be determined by drawing lines from the leading edge of stains through the long axis. The lines come together in a general area where the blood has emerged, helping to locate the origin of the bloodstains.