The use of blood pattern analysis work at crime scenes has had an increasingly high profile over the last decade. In line with this the need for scene examiners to appreciate the complex nature of stains and the terminology used has also increased. Included below are brief notes on some of the most common stains encountered at scenes and also a short explanation of terms.
Information that may be gained from the examination of a scene where blood staining is present can be complex but may give vital clues as to what has occurred.
Scientists called out to scenes may be able to give information on the nature of the offence that has taken place or the location of the initial site of an attack. In some cases the number of blows landed during an attack and the positions of victims/assailants can be calculated, along with the likelihood of blood on an assailant. Information on the sequence of events can also be used to support or refute a suspect’s account.
Many of the terms now used internationally regarding Blood Pattern Analysis (BPA) have been standardised by the International Association of Blood Pattern Analysts (IABPA).
Single Drops develop due to a sufficient volume of liquid blood being able to overcome surface tension and the effects of gravity upon the liquid blood. This can also occur where sufficient force acts upon the blood to overcome the surface tension. When this occurs, blood forms into spherical drops that will only break up if they come into contact with another drop or surface. When the drop hits a surface the resultant stain will be affected by the angle of impact and also by the nature of the surface the drop strikes (see Fig. 1). If the angle of impact is sufficient an associated stain known as wave cast-off is formed (see Fig. 2).
Fig (1) -Rough surface
Fig (2)-Angle of impact
Wave cast off
Impact spatter is a type of blood staining seen at crime scenes. This type of staining results from one or more blows/impacts into wet blood causing a random distribution of size of blood stain with many of the resultant stains showing clear directionality. With this type of spatter the staining will be increasingly concentrated towards the area of impact. This site of impact (or area of convergence) can be determined using a technique called stringing which can give a three-dimensional aspect to the interpretation. This employs multiple stains with clear directionality to ascertain the direction of flight, then by calculating the length and width of the stain the angle of impact can be gauged.
Sometimes associated with impact spatter is cast-off staining. This will often appear as in-line staining when blood is cast or flung from a moving object due to a change in velocity or direction. This particular type of staining can give vital clues as to the events that have taken place during an incident.
An individual that has arterial damage can quickly lose large amounts of blood. The subsequent staining will depend on numerous factors including the extent of damage, interference of clothing and blood pressure.
The main types of arterial staining seen are:
· Arterial gushing – caused when blood under pressure exits an artery with a large volume of blood being projected onto one particular area, typically the staining will run (due to gravity) on vertical surfaces (Fig. 3).
· Arterial spurting – caused when blood exits under fluctuating pressure forming distinctive ‘S’ or ‘W’ patterns (Fig. 4).
· Arterial rain – caused when blood exits a breached artery under pressure and is allowed to fall due to gravity onto a horizontal surface, resulting round blood stains can be seen (Fig. 5).
Fig (3)
Fig (4)
Fig (5)
