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Criminal investigation: Death investigation - Stabbing
From petty crimes to major crimes one of the many roles of any Police Force is to investigate criminal activity. Investigations take on two principle forms, reactive and proactive investigations (Kilfeather, 2011). In the following paper I am going to discuss the phases through which a death by stabbing investigation may go through from when the incident is reported or encountered, to its term once the case is closed and the perpetrator has been prosecuted through trial and possible appeals (Kilfeather, 2011).
Incidents where a crime is reported to the police are reactionary. In a typical incident a call is received at an emergency call centre where further information is requested and officers are dispatched to the scene. It is of extreme importance that the dispatcher relays all the information received to the officers who have been dispatched. In the following scenario a call is received by the dispatcher that a stabbing has occurred.
Once the call is received the dispatcher will initiate patrols in the area by broadcasting the incident to officers in the area, the call is logged into a central information store and specialised units and personnel (such as the crime scene investigator on duty and forensic units) are notified that an incident may be occurring. The dispatcher continues to maintain the flow of information between initial response personnel and the crime scene investigator on duty until the scene is handed over. (Kilfeather, 2011)
Much depends on whether an investigation is successful or not in what is done by the initial responding officers on the scene (Kilfeather, 2011). On arriving at the scene notes should be taken as to the date and time of arrival, weather conditions, persons on the scene and the number plates of any vehicles in the vicinity that may be related to the crime. Once this is done the officers should stop, look, listen and smell to see that the scene is free from any dangers, they must also assume that the crime is still in commission and that the perpetrators may either be at the scene or trying to flee the scene (Reno, Marcus, Robinson, Brennan, & Travis, 2000). Once the scene has been assessed the officer’s priority is to control and preserve the scene. Supervisors need to be contacted and updated about the situation, additional specialised personnel should be contacted so that they may be readied for action. The area should be treated as a crime scene until determined otherwise by the assigned crime scene investigator. The first priority is the safety of the officers and that of the persons at the scene while keeping in mind the prevention of contamination to any potential evidence (Reno, Marcus, Robinson, Brennan, & Travis, 2000). If emergency personnel arrive after the officers, they are to be taken to the victim through an indirect path so as to contaminate the scene as little as possible. If the victim is still alive, emergency personnel are to be asked to handle any items that may later become evidence in a manner as to contaminate the evidence as little as possible. Any tears, punctures or stains in clothing should be not be cut through but cut around in order to be preserved. Clothing and any personal effects are to be stowed away in evidence bags or kept safe until follow up personnel arrive at the scene. No clean-up of the area should be performed by any personnel, any items, including packaging of items used in order to try and save the victim’s life should be left on site and notes taken as to what was used and how. If the victim is still alive at the scene the officers should attempt to take a dying statement from the victim (Reno, Marcus, Robinson, Brennan, & Travis, 2000).
If any persons are found on the scene they must be assessed to determine if they are witnesses to the incident or if they are potentially the perpetrators. Personal details are to be taken of all the persons found at the scene, witnesses separated from suspects and all persons not involved in processing or protecting the scene moved away (Reno, Marcus, Robinson, Brennan, & Travis, 2000).
The crime scene
Once the incident has been confirmed and a primary crime scene established the crime scene investigator will immediately go to the scene in order to take over the investigation (Holder, Robinson, & Laub, 2011). Once on the scene the crime scene investigator will identify themselves and establish who the essential personnel are on the scene. The crime scene investigator will get a preliminary debriefing from the first attending officer and then establish the perimeter of the crime scene depending on whether a secondary crime scene has been found or to decrease the area required to be protected. Once the victim is pronounced dead by the medical personnel the scene is immediately turned over to the crime scene investigator who will call for the assistance of various forensic experts depending on the situation (Holder, Robinson, & Laub, 2011).
In fatal stabbing incidents a number of facts may determine the direction in which to proceed with the investigation. The number and kind of wounds sustained by the victim could determine what type of an attack the victim was involved in. Stab wounds are characterised by some or all of the following features.
A stab wound is a cut or incision where the width of the injury on the surface of the body is less than the depth. These wounds are inflicted using thrusting action with a pointed object (Stab wounds, 2014). Stab wounds are typically characterised by clean cut edges with pointed ends (Figure 1), if an end is not pointed it may possibly have a fish tail or boat shaped look (Figure 2). It would also be rare that a weapon would enter the body and be removed along the same axis. This ratcheting motion will cause notching showing a change in direction of the knife or body. Some wounds may appear to gape open depending on the direction of the incision made in relation to the Langer or cleavage lines (Figure 3). Often the cross section of the weapon will match the wound at the point of entry. Underlying bone may be scored or broken and abrasions or bruising may be present at the wound site (Stab wounds, 2014).
In order to assess the wound dimensions the length of the wound should be measured to the nearest millimetre. Any attempt to match the weapon used with the dimensions of the injuries sustained wound be fraught with inaccuracies due to the elasticity of the skin. On withdrawal of the weapon the skin would shrink by up to 2 millimetres, also if the weapon was thrust into the body at an oblique angle the width of the entry wound may be wider than expected. Solid organs retain more weapon characteristics as they do not tend to deform or change shape.
The documentation of the wounds should be undertaken in terms of their anatomical position and to their relative position to an anatomical landmark. Pre-printed body diagrams such as those used in post mortem autopsy investigations and the use of digital photography make excellent additions to the medical notes (Figure 5).
Wounds are known to gape open depending on their anatomical location and the direction of the incision. This said not all wounds comply with the same characteristics. Conical weapons may produce linear wounds and the direction of the wound may differ in different parts of the body (Stab wounds, 2014). Also the cross section of the wound will only correspond to the length of blade that entered the skin. If a weapon did not penetrate the skin entirely only the proportion of the weapon that entered may relate to the wound tract. Another point to eep in mind is that the position of the body and whether the muscles were tensed or relaxed may produce nonlinear wound tracts in which the wound may be in the form of a zigzag fashion (Stab wounds, 2014).
Different weapons will produce different wound characteristics. Knives such as kitchen knives that have one cutting edge will produce a wound with a clearly pointed edge on one side while the other will have a split or squared off shape. Split ends can also be caused using double edged weapons where the knife is rocked back and forth in the wound (Stab wounds, 2014). Serrated blades cannot usually be distinguished from straight edged blades unless the blade was drawn over the skin (Figure 4). Double edged blades produce a wound with pointed edges or a spindle shaped slit at both ends (Stab wounds, 2014). Weapons with blade guards or hilts may produce distinctive bruising where the guard impacts the skin, especially in points on the body where the skin is supported by an internal structure such as the rib cage. Similar bruising may be found in cases where although the weapon had not guard, the attacker’s fist would have impacted the victim in a similar fashion (Stab wounds, 2014).
Knives are not the only weapons used in stabbing incidents. Other weapons of opportunity such as glass, chisels or even blunter objects like screwdrivers may have been used in the incident. Items such as a Philips or torques head screwdriver may produce wounds that are star shaped, however blunt rectangular or square shaped objects may also produce stellate patterns. One must exercise an utmost caution when interpreting these kinds of wounds (Stab wounds, 2014).
Some stab wounds may be wrongly interpreted as being small calibre gunshot wounds. Weapons such as ice picks or a welding flux hammer may produce rounded wounds with abraded edges (Stab wounds, 2014).
In any stabbing incident unless the victim is restrained it is rare that a weapon enters the victim’s body at the same angle as it exits. Both the assailant and the victim wold be in a highly charged state where each of their movements may be highly fluid. The wounds inflicted would reflect this scenario and would often be irregular and V shaped. Other movements such as twisting or rocking movements made in order to retract the weapon will also distort the shape of the wound making it much larger that would otherwise show for if the same weapon were used in a more static scenario (Stab wounds, 2014).
The human body in made up of a number of cavities that would compress under the force of an attack. This compression can complicate the estimation of the length of a weapon used in relation to the wound inflicted. Also different weapons may have a varied cross section along their length. A crowbar for example may have a rounded point that turns into a square cross section, this may produce wounds that are circular where the weapon was not thrust fully into the body and stellate where the weapon enters to the point of its square cross section. (Stab wounds, 2014)
The positions of the assailant and the victim are highly important in order to be able to reconstruct the scenario. Tears in clothing, small cuts near the wound tract, bruising and abrasions may all give indications to the direction in which the weapon was thrust. Invasive use of probes, latex solutions and others in trying to determine the wound tract are not satisfactory as they may either damage the tract further or the liquid solutions may leak into other body cavities. Non-invasive techniques such as using MRI scans and x-ray provide better solutions in order to better view the wound tract dimensions and shape (Stab wounds, 2014).
Forensic pathologists often use a rough scale to measure the force required to inflict a stab wound. Three degrees of force are used in this scale, mild pressure, moderate force and extreme force. Research has shown that only the skin offers any major resistance to penetrate a body cavity. Therefore in order for a weapon to penetrate a victim’s body only the tip of the weapon needs to be sharp. Some areas of skin are easier to puncture than others due to the skin being stretched as with the chest wall (Stab wounds, 2014).
Very little force is required to penetrate the skin. Research has found that a force of as little as 5 N is all that is required, while a person can generate more than 2000 N of force on the axis of a weapon. Overhand strikes create more cutting force than swiping or slashing style thrusts (Stab wounds, 2014).
The amount of time that a victim is likely to survive after being stabbed can assist in the reconstruction of the scenario. This however is very difficult to ascertain, some victims succumb quickly to wounds while others are still very capable of strenuous activity after they have been stabbed in similar a manner (Stab wounds, 2014).
Arrest and trial
In order to bring a suspect to trial, the investigator must keep all documentation and evidence safe from manipulation. Each person involved in processing the scene must be debriefed. All evidence moved to safe keeping and the chain of custody established from crime scene collection through processing and to safe keeping. Jurisdiction over the body is maintained until the crime scene investigator sees fit. Only once the crime scene investigator is satisfied with the collection of evidence from the body, including any tests, autopsy results toxicology and others will the body be released. (Holder, Robinson, & Laub, 2011)
In any investigation there are numerous procedures that need to be followed. Adherence to these procedures is required in order to make the evidence collected stick in a court of law. These procedures can be summarised as follows
- Initial response and prioritisation of efforts
- Preliminary documentation and scene evaluation
- Scene processing
- Debriefing of those involved, documentation and recording the incident
Figure 1 Knife wound impressions
Figure 2 Wound impressions
Figure 3 Langer Lines
Figure 4 Serrated blade impressons
Figure 5 Post mortem exam autopsy
Hess, K. M., & Orthmann, C. H. (2010). Criminal Investigation 9th Edition. New York: Cengage Learning.
Holder, E. H., Robinson, L. O., & Laub, J. H. (2011). Death Investigation: A guide for the scene investigator. Washington: U.S. Department of Justice.
Kilfeather, R. F. (2011). Managing and coordinating major criminal investigations 2nd Edition. London, New York: CRC Press.
Reno, J., Marcus, D., Robinson, L., Brennan, N., & Travis, J. (2000). Crime Scene Investigation - A guide of law enforcement. Washington: Department of Justice Response Center.
Stab wounds. (2014, 05 05). Retrieved from Forensic medicine for medical students: http://www.forensicmed.co.uk/wounds/sharp-force-trauma/stab-wounds/