In the first of a series of articles on forensics, Adam Marsh, of Essential Forensics, a Professional Forensic Science Company which helps with various types of legal cases shares his insight on blood staining and clothing analysis. Interesting and insightful aspects which many of you crime fiction writers and readers will find fascinating. You can visit Essential Forensics HERE
Blood staining and clothing analysis is a specialised area of forensics. Forensic investigators are experienced in attending crime scenes collecting and preserving incriminating evidence. They use a specific forensic process to ensure that they gather as much information as possible. Blood and fibre samples, photographs and precise measurements are taken allowing them to reconstruct exactly what happened at the scene of the crime. Blood typing and DNA recognition can be carried out from the droplets collected. Forensic scientists will examine the characteristics of the size, shape, and distribution of the blood spatter. Blood spatter can be from the perpetrator or the assailant, each sample must be identified to be able to calculate how far the blood has traveled, indicating force used and from which direction. This combined information allows an accurate reconstruct of the crime.
When blood exits the body it appears to be a bright red colour, as time passes the colour alters. Highly oxygenated blood makes the haemoglobin bright red and deoxygenated blood causes the haemoglobin to turn much darker in colour. These findings allow the forensic investigator to estimate the time of an incident along with details of what may have happened, a series of events can be created from the spatter patterns, volumes of blood and colour. The positions of people involved during an attack/incident can be identified using the available evidence, this information assists the police investigations proving or disproving witness statements ensuring appropriate convictions are made.
An experienced forensic specialist can detect if a crime scene has been tampered with by examining available blood patterns. Objects at the scene can create barriers preventing spatter from depositing on certain surfaces or in certain directions, therefore any moved furniture, opened or closed doors and moved objects can be identified suggesting the scene has been manipulated, maybe in an attempt to destroy evidence.
Latent blood staining, or attempts to clean up a crime scene, can also be identified. Latent blood samples are droplets of blood that are not visible to the naked eye. As part of any crime scene investigation the investigator will be looking for latent staining. These stains can be as a result of somebody trying to clean up the area purposely or as a result of accidental contamination. It is vital that once a latent blood sample is suspected samples are taken prior to the forensic testing used to confirm that it is actually blood, the reason being the tests used can interfere with blood typing and DNA preservation. Chemical such as Phenolphthalein, Leucomalachite, Luminol, Blue Star, Lumiscene are the chemicals used when identifying latent blood samples making them visible. Latent prints can reveal footprints, fingerprints or detect any objects being moved. Establishing the patterns and directions of any prints can add vital information to the investigation.
Blood stains and patterns are classified into three main categories
Low velocity spatter
Drip stains and patterns are found where less force is used. A low velocity spatter is usually the result of dripping blood. The force of impact is usually five feet per second or less, and the size of the droplets is somewhere between four and eight millimetres. For example after a stabbing or other low impact trauma, then walking away from the scene, droplets of blood creates a trail of blood which can be used to account for some of the crime scene and establish what has happened.
Transfer stains and patterns
Blood contaminated surfaces, fingerprints, footprints or objects such as weapons can be identified by this pattern. Establishing these can help Forensics experts and Crime Scene Investigators to identify the timeline after a wounding, such as some of the movements made.
High velocity splatters
These patterns are commonly caused by gunshot wounds, although they can be caused by other weapons if the assailant exerts an extreme amount of force. They travel at more than 100 feet per second and usually look like a fine spray of tiny droplets.
Bloodshed and blood pattern recognition is a study of the physical and biological properties of any traces of blood from the crime scene or on any implements, weapons or fabrics involved during such incidents. It is essential that a detailed examination of the crime scene along with surrounding areas are carried out promptly, any delay at this stage can result in the objects being moved or becoming contaminated reducing the effectiveness and reliability of the evidence. The person carrying out the forensic investigation will produce a detailed report documenting all findings. Blood staining and clothing analysis often produces crucial evidence making it an invaluable source of incriminating evidence in any criminal investigation.