Wipes and Swipes in Bloodstain Pattern Analysis

If you are a regular reader of this blog you know that the examination of bloodstain patterns is a crucial step in reconstructing the events of a crime. A proper examination of bloodstain patterns may reveal such things as the number of bleeding subjects, types or locations of injuries, sequencing of events, movements of bleeding subjects, and minimum number of blows to name a few.  One category of bloodstain patterns are what I refer to as contact transfer. Two of these types of stains are called wipes and swipes and they can be very useful in crime scene reconstruction. Here is how the scientific working group on bloodstain pattern analysis (SWGSTAIN) defines them.

Swipe Pattern:

A bloodstain pattern resulting from the transfer of blood from a blood-bearing surface onto another surface, with characteristics that indicate relative motion between the two surfaces. 

In simple terms this means that a bloodstained item like a hand comes into contact with a non-bloodied (clean) surface and said pattern indicates a direction of travel. Swipes can be used to reconstruct the movement of persons in a scene as well as indicate the location of injuries in some cases. In the picture below you will see a large swipe on a bathroom wall adjacent to the tub. There are also swipe stains on the edge of the tub and the heating vent on the floor. The victim was present on scene so it was pretty easy to correlate the injuries with the swipe stains but had the body been removed (or left on their own power) an analyst could reconstruct the events with some reliability. You’ll notice the area on the wall is quite large and there is an “arch” shape to it. This individual had a large amount of blood on the right shoulder and back as well as both hands. They collapsed against the wall with their right shoulder and slid downward. They also placed a bloody right forearm and hands on the edge of the tub.  As a writer you should consider the location of  your character’s bleeding injuries. If they have bloody hands and they open a door then they are going to leave stains either on the handle or on the edge of the door (or both). If they are bleeding from a gunshot wound to the leg and drive a car there will be blood on the driver’s seat. If you really want to get serious you can place some ketchup on an area of your body/clothing and then re-enact their actions to see where the staining will occur (note: we would never use ketchup in CSI work but it it easier to clean up then blood).

Wipe Pattern:

An altered bloodstain pattern resulting from an object moving through a preexisting wet bloodstain.

A wipe pattern is usually created when an object (bloody or clean) makes contact with a wet bloodstain and alters its appearance in the process. So if you have blood spatter on a wall and then a person’s hand wipes through the pattern it will leave evidence of that contact in the deformation of the original stain. Obviously this is an indicator of sequencing events. The event creating the original stain occurred before the event creating the wipe pattern.  Imagine you have blood droplets on a tile floor and sometime after that the victim’s body is dragged across that floor. The original blood droplets may have a skeletonized appearance which may even indicate a minimum elapsed time between the two events.  The image below shows an existing mixed passive and impact spatter pattern that has had a clean cloth wiped across the surface from left to right.

As writers you may not want to get into this level of discussion in your storyline but using the proper terminology will go a long way with knowledgeable readers. The important thing to remember is that bleeding subjects are usually going to leave behind bloodstain patterns, especially when they make contact with another surface. Consider how that will look in your crime scene setting and what deductions your characters can draw from it.