Transfer, Wipe, Swipe, and Void Patterns: Interpretation and Documentation

What Contact Patterns Tell Investigators

When a blood-bearing surface touches another surface, it leaves a record of that contact. These contact or transfer patterns are among the most information-rich evidence at a crime scene because they can reveal what objects were present, how they moved, and in what sequence events occurred. The International Association of Bloodstain Pattern Analysis (IABPA) provides standardized terminology that all forensic technicians must use so that reports, court testimony, and peer review are consistent across jurisdictions.

Transfer Patterns

A transfer pattern is produced when a bloody surface contacts a second surface and deposits blood onto it. The result may carry the texture, shape, or outline of the original surface — a shoe sole, a gloved hand, a fabric weave — making object identification possible. The transferred image is sometimes called a contact pattern when it reproduces recognizable detail.

When documenting a transfer pattern, describe:

• The overall shape and dimensions
• Any texture detail visible (tread, fabric grain, ridge detail)
• The apparent surface that made contact
• The quantity of blood deposited (heavy, medium, light)
• Whether the pattern is singular or shows repetition suggesting multiple contacts

Wipe Patterns

A wipe pattern forms when an object moves through an existing wet bloodstain, displacing and smearing blood in the direction of travel. The leading edge of a wipe is typically well-defined and may show a feathered or scalloped border, while the trailing edge is diffuse. The direction of movement is read from the heavier, more defined margin toward the lighter, thinning end.

Wipe patterns tell reconstructors that a bloody object — a hand, a shoe, a piece of clothing — moved across the surface after blood was already present. They are important for sequencing: the underlying stain must have preceded the wipe.

Swipe Patterns

A swipe pattern is produced when a bloody object moves across a surface that was not previously bloodstained, depositing blood as it travels. Visually, swipes and wipes can look similar, but the distinction matters for reconstruction. In a swipe, blood is added to a clean surface; in a wipe, an existing pool or stain is altered.

In practice, determine which pattern type is present by examining context: is there underlying staining beneath the smear, or did the blood originate entirely from the moving object? The IABPA glossary defines these as distinct categories, and using the wrong term in a report or on the stand undermines credibility.

Key documentation points for both wipe and swipe:

• Direction of travel (indicate with a measured arrow on sketches and photographs)
• Width of the smear at its widest and narrowest points
• Presence of recognizable object detail within the smear
• Relationship to surrounding stains for sequencing

Void Patterns

A void pattern is an area within a bloodstain distribution where blood is absent because an object blocked the blood's path or was removed after blood was deposited around it. Voids are among the most powerful reconstruction tools because they reveal that something — or someone — was present during the bloodshed event and was later moved or removed.

There are two common void situations:

1. Projection void: An object blocked spatter in flight, leaving a clean silhouette surrounded by spatter. The shape of the void may outline the object.

2. Contact void: An object rested on a bloodstained surface and was then removed, leaving an unstained area whose shape reflects the object's footprint.

When documenting a void:

• Sketch the void's exact boundaries and measure its dimensions
• Describe its geometric shape and any recognizable outline
• Note whether surrounding stains show directionality pointing toward or away from the void
• State what class of object (size, shape, possible type) the void suggests — but do not name a specific object unless physical evidence supports it

Writing a Pattern Narrative for Court

Every pattern description you produce must meet courtroom documentation standards. That means:

• Use IABPA terminology exactly — "wipe pattern" not "smear," "void" not "clean spot"
• Describe before interpreting — state what you observe, then what it indicates
• Avoid unsupported conclusions — write "consistent with" or "suggests" rather than "proves"
• Include measurements and orientation — north, south, relative to a fixed reference point
• Note the condition of the pattern — wet, dry, partially disturbed

A model sentence: "A wipe pattern approximately 18 cm long and 4 cm wide is present on the south face of the kitchen cabinet, with the heavier defined margin at the west end, indicating movement of a bloody object from west to east."

Safety Reminders

Even with simulated blood, treat all wet biological simulants as if they were potentially infectious. Wear nitrile gloves throughout the hands-on activities. If any real biological material is involved in a training scenario, a face shield and fluid-resistant gown are required per standard bloodborne pathogen precautions. Dispose of contaminated card stock and swatches in a designated waste container. Wash hands thoroughly after removing gloves.