When investigating incidents of particular crimes or vehicle collisions, it may not be known exactly what has occurred due to lack of evidence or lack of witnesses. Forensic reconstruction is essentially the process of establishing a sequence of events about the occurrences during and after a crime or other incident through the study, analysis and interpretation of evidence. Through scientific method, gathered information, logical reasoning, and experience, events may be established, whether through a simple mental exercise or an elaborate re-enactment. The resulting reconstruction will hopefully be used to clarify the sequence of events and even jog the memories of victims and witnesses who were present at the time. If being used to help witnesses remember, the reconstruction will often take place at the same time, in the same place, and on the same day so as to recreate the event as accurately as possible.
Forensic reconstruction can be divided into three primary specialties. Specific incident reconstruction involves the re-enactment of the entire event, commonly employed during the investigation of a traffic accident or bombings. Specific event reconstruction focuses specifically on a precise event. And specific physical evidence reconstruction relates to the reconstruction of the likes of blood spatter or firearm use.
The reconstruction may often begin with a simple walkthrough of the scene at which the incident occurred. The investigator may be able to construct a rough hypothesis of what happened, why it happened, and how. The scene is fully documented through note-taking, photography, video recording, and sketching. Evidence will be thoroughly located and collected for analysis. Any victims or witnesses will be interviewed and detailed statements taken. All of this information will be vital in the accurate reconstruction of the incident.
The final reconstruction will utilise all available evidence and information to give a detailed account of what is most likely to have occurred. This will include events before, during and after the incident, with the location, position and actions of anyone involved. If successful, it should give indication as to how and why the incident took place. It is likely that the investigator's reconstruction will be challenged in court, particularly as there are so many variables and possible outcomes to be taken into consideration. It may never be completely clear exactly what happened, so there may always be doubt regarding the accuracy of the reconstruction.
Individual pieces of evidence may prove vital in crime scene reconstructions, particularly blood spatter evidence, firearm evidence, and road traffic collisions.
Bloodstain patterns in particular are vital in the reconstruction of violent, bloody crime scenes. Blood follows very specific laws of physics, and so the shape and distribution of bloodstains can be used to establish the behaviour of the blood and ultimately the events which occurred. When blood patterns are found at an incident scene, reconstruction methods can be used in attempts to recreate those patterns and thus ascertain how they were originally created during the incident.
Shooting incidents are also commonly subjected to crime scene reconstruction techniques. Experimental shootings will often be conducted in order to establish details such as the distance from which a firearm was discharged and where the shooter was positioned at the time of the incident.
Vehicle Collision Reconstruction
Reconstructions are often conducted during the investigation of road traffic collisions. When such an incident occurs it is vital to conduct a thorough investigation, particularly if a crime has taken place, an individual has been killed, or there is debate over who is responsible for the collision. Unfortunately the scene of a road traffic collision is often cleared away quickly so as to cause minimal disturbance to traffic, so reconstructions are often relied upon to establish a sequence of events.
As much evidence as possible is collected from the scene itself, including vehicles involved, eyewitness reports, photographs, detailed sketches, any video footage available, information on weather conditions, and any known details regarding the positions and velocities of vehicles involved. The investigation will often start from the end and work backwards, as the final positions of vehicles involved are generally known, though witness statements and videos may give information on the velocities and actions of the vehicles.
Fundamental laws of physics are often followed during the investigation of vehicle collisions; the laws of conservation of energy and momentum. The law of conservation of energy, based on Newton's third law of motion, states that energy is neither created nor destroyed but can be converted into different forms of energy. A moving vehicle has kinetic energy. If a collision occurs, this energy will be dissipated either against the road when the vehicle skids, or upon striking a surface or object, causing deformation of the vehicles or injury to the pedestrian. Based on this law of conservation of energy, the energy prior to impact will remain in existence but be converted into other forms of energy. Momentum relates to the vehicle's mass and velocity. Similarly, the law of conservation of momentum states that the total momentum of all vehicles involved will stay the same, though the momentum of the individual vehicles will change. As an example, if a stationary vehicle is hit by a moving vehicle, the stationary vehicle will gain momentum and the moving vehicle will lose it, though overall momentum will remain the same. By calculating and analysing the energy and momentum of vehicles and pedestrians, it is possible to establish the initial and final velocities of those involved, thus establishing the sequence of events. This can ultimately help determine whether a vehicle was moving too fast, where another vehicle or pedestrian was positioned at the time of the collision, and essentially who, if anyone, is to blame for the incident.
On the most basic level, accurate measurements, known facts or possibilities can be input into the computer and the software instructed to generate conclusions based upon these assumptions. Animation and computer-aided design (CAD) software can produce images of crime scenes and vehicle collisions, running through various possible scenarios until the most likely sequence of events is established. Such programs allow for an endless number of factors to be taken into account, such as weather conditions and the actions of individuals that may have had an impact on the outcome of the incident.
Whereas computer software reconstructions can aid investigators in piecing together the sequence of events, the scenarios produced can also be used to jog the memories of witnesses. By seeing a visual representation of the incident, they may remember additional information or be able to correct inconsistencies in the currently assumed sequence of events. The reconstructions produced by the software are also ideal for use in court when attempting to explain to the jury how the crime or vehicle collision is likely to have occurred. However computer software simulation is often placed under greater scrutiny than physical reconstructions. When acting as an expert witness using computer simulations, the expert must be able to explain the mechanisms of the software itself, what computer systems were used, where the inputted information was gathered from, and what the outcome shows.
Evidence dynamics refers to any influence that may change, obscure, or obliterate physical evidence, whether accidentally or maliciously. If a piece of evidence is compromised in any way, it must be established when and how. Specific physical evidence reconstruction can be used to trace any alterations made to evidence, later allowing forensic reconstruction of the scene as a whole to be carried out. There are various possible influences to be taken into consideration under evidence dynamics.
1) Offender Actions - The actions of an offender both during the crime and after. This may include precautionary acts, those which consciously attempt to confuse investigators, hide the offender's identity or connections, or conceal the crime itself. Ritual or fantasy acts are those carried out by the offender for their own personal reasons, such as necrophilia and post-mortem mutilation. Staging involves acts performed by the offender to purposely deflect suspicion from them, such as incriminating someone else.
2) Victim Actions - Activities performed prior to or following the crime. These may influence the integrity of evidence, such as cleaning up of the crime scene after the crime, or the victim showering after an attack. Such actions may compromise or even eliminate vital evidence.
3) Secondary Transfer - This is the exchange of evidence between objects or persons that occurs following an original exchange. Such transfers may be useful in establishing routes taken by suspects or victims.
4) Witness Actions - The actions of witnesses, usually after a crime has occurred. This may include preserving victim dignity by covering their body or, more maliciously, the theft of items from the scene. Though these may seem harmless to the witness at the time, these acts have the potential to damage or destroy evidence.
5) Natural Activity - The activity of weather, insects and animals can also affect evidence. These should be taken into account during the reconstruction of a crime, though this may be particularly difficult due to the numerous possible factors.
6) Emergency Service Actions â€“ Police, fire-fighters and paramedics can all alter or damage evidence during life-saving efforts. Such actions will often occur at the very beginning of an investigation, therefore the results may often be mistaken for being related to the crime itself.