A ligature mark is a physical impression or injury left on the body, most often the neck, caused by the application of a constricting band or material. This injury results from pressure applied by an object like a rope, wire, belt, or piece of fabric tightened around the skin. In forensic investigations, these marks serve as significant evidence, helping to determine the cause and circumstances surrounding a constriction injury. Forensic experts use the unique characteristics of the mark to reconstruct the event, providing insights into the type of material used and the force applied.
How Ligature Marks Form
The formation of a ligature mark begins with the mechanical compression of the skin and underlying soft tissues. When a material is tightly wrapped, the pressure forces blood out of superficial capillaries, initially causing a pale or blanched furrow. Continued pressure and friction damage the epidermis, leading to an abrasion within the groove. This injury often results in the skin drying out, giving the mark a hardened, yellowish-brown, and parchment-like appearance.
The physical characteristics of the mark are directly influenced by the nature of the material used. For example, a thin wire creates a sharp, deep indentation, while a soft, wide cloth might leave a broader, fainter impression. Rough materials, such as a braided rope, often transfer their specific pattern onto the skin, creating an imprint that can be matched to the object. The depth and clarity of the mark also reflect the duration and intensity of the pressure, with greater force producing a more defined indentation.
Interpreting the Mark and Cause of Death
Forensic analysis focuses on distinguishing between injuries caused by hanging and those caused by ligature strangulation, as this distinction suggests the manner of death. Marks from hanging are typically situated high on the neck, often above the thyroid cartilage, and run obliquely upward toward a suspension point, creating an inverted V-shape. Since the knot prevents the material from completely encircling the neck, the mark is often discontinuous, with a break opposite the point of suspension.
In contrast, a mark resulting from ligature strangulation is commonly found lower on the neck, often below the thyroid cartilage. This mark tends to be transverse, or horizontal, and completely encircles the neck because the force is applied externally, not by the body’s weight. The continuous, horizontal nature of the mark indicates an externally applied constricting force.
Other features of the mark help inform the interpretation of the event. Petechial hemorrhages, which are tiny, ruptured capillaries visible on the skin, particularly the eyelids and face, suggest a restriction of venous blood flow from the head, frequently associated with strangulation. The vitality of the injury—whether it occurred before or after death—is assessed by examining signs of a biological response, such as bruising or inflammation. An injury inflicted while a person is alive often shows distinct tissue damage and an inflammatory reaction that is absent in postmortem injuries.
Medical and Forensic Examination
The thorough examination of a ligature mark begins with meticulous external documentation at the scene and during the medical autopsy. Detailed photographs are taken from multiple angles, often using specialized lighting like Forensic Light Sources (FLS) to reveal subtle bruising or impressions. Measurements of the mark’s width, depth, and distance from fixed anatomical points are recorded to establish its precise location and characteristics.
A significant part of the external examination involves the collection of trace evidence from the mark itself. Fibers, hairs, skin cells, or DNA from an assailant can be transferred to the constricted area or the ligature material. The material used to create the mark, if present, is collected, preserved, and analyzed to match any patterned impression left on the skin.
The internal examination performed by the medical examiner confirms the extent of the injury beneath the skin. The soft tissues of the neck are dissected and examined for deep tissue hemorrhage or contusion, which is often pronounced in ligature strangulation cases. Blood extravasation beneath the mark indicates that the injury occurred while the heart was still pumping, confirming its antemortem nature. Pathologists also look for fractures of the laryngeal cartilages or the hyoid bone, as these injuries are frequently associated with violent neck compression.