7.1: The Discovery and Preservation Process

Critical to the discovery of evidence, and the subsequent preservation of that evidence, is the ability to quickly stop all movement that could potentially damage or destroy the evidence in the scene of a crime. This responsibility falls on the first responding law enforcement personnel to arrive on the scene. The first responder has a very essential role in crime scene investigation and processing. Without proper preservation of the crime scene, there may be no crime scene to process. The responsibilities of the first responder includes: controlling the scene, affecting custody of the suspect if present, if not, to broadcast a description and direction of travel to other responding officer; locating victims; interviewing witnesses; and making the scene safe for fire, ambulance, and crime scene personnel, while evacuating the scene of unessential or unaffected people, thus preserving perishable and transient evidence. Perishable evidence is that which can be easily disturbed or destroyed, like impression evidence or bloodstains. Transient evidence is that which may move or dissipate, like a piece of paper bearing a threat or criminal intentions, which can be blown away by the wind or damaged by rain. The first officer on the scene must also determine the extent of the crime scene, with consideration to avenues of ingress and egress of the suspect, ensure that emergency medical services personnel do not destroy important aspects of the scene, stretch crime scene tape, and make the necessary notifications to request detectives and crime scene investigations personnel to respond to the scene. It is also up to the first officer on the scene to render aid to those requiring medical assistance while awaiting the arrival of the emergency medical services. Saving a human life or preventing additional injury is a primary responsibility of law enforcement, and it may be said that it is far better to save a life than an item of evidence. However, it is possible to maintain the integrity of scene, and the evidence it contains, as much as possible while rendering that aid. The officer must use discretion and first aid knowledge to balance the need for medical aid, but with the knowledge that the evidence must be preserved. Once all of this is done, the officer must start a crime scene log, which is a record of all personnel who were in the scene before and after the perimeter was established, and the purpose for their presence in the scene.

Guns and Other Weapons

The first responder should not examine or touch the contents of the crime scene unless the evidence is perishable or transient and will be lost if not immediately recovered. Weapons used in the commission of a crime should only be collected if the area cannot be contained and there is a possibility that the item may be used by the suspect or other actors against peace officers or other persons. In this event, the weapon must be retrieved paying particular attention not to disturb fingerprint, blood, or hair and fiber evidence and, if possible, to prevent contamination. The weapon must never be returned to the crime scene if it is removed by the first responder. Weapons used in the commission of the crime should remain in the crime scene, untouched, provided it is safe to do so. Never disturb a firearm or “render it safe” before the arrival of crime scene technicians. Post security by the weapon until such time as the crime scene technician can collect DNA specimen, and only then prepare the weapon for evidence packaging. On one occasion, your author arrived at the scene of a homicide where a gun had been found near the body of the decedent. Unfortunately, the gun was immediately collected by the first officer to arrive on the scene, and rendered “safe” with ungloved hands, and thrown on top of his duty jacket in the trunk of his patrol car. Your author asked the officer to explain his actions, to which the officer responded that he was worried the gun would be “picked up.” “By whom? The decedent?” was your author’s response. The gun was dropped by the suspect in his haste to escape the scene. The obvious court challenge was had the DNA that was recovered from the gun been deposited by the suspect or was it transferred from the contact with the jacket in the trunk? Every law enforcement officer should be trained to consider the potential for destroying or contaminating critical evidence before handling any weapon found at the scene of a crime.

Scene Contamination

Gone are the days when a detective or crime scene investigator enters a crime scene with a cigar in their mouth, wearing short sleeves, and beshoed with their favorite pair of tennis shoes. We must remember that a suspect may leave touch DNA in a crime scene, but the detective or crime scene technician too may inadvertently contribute our own DNA in the exact same place. It is suggested that humans shed upwards of 400,000 epithelial skin cells in a 24-hour period, which by your author’s maths is almost 278 cells every second that you are in the crime scene. The suspect who wore gloves, a hat, a mask, a long-sleeve shirt and spent three minutes in the crime scene, will invariably contribute far fewer cells than the detective or crime scene technician who is not wearing a mask, has no gloves, is not wearing head covering, is wearing a short-sleeved shirt, and spends an hour in the crime scene. Although there is no such thing as an uncontaminated crime scene (unless someone at the forensic lab murders their supervisor in the sterile evidence examination room), it is important to make every effort to mitigate further contamination and to prevent cross-contamination of evidence. Protective clothing must always be worn (face mask, shoe coverings, latex gloves, etc.) and great effort should be made not to handle items of evidence before they have been documented and photographed, and only after changing gloves between each item of evidence handled. This is also very important for patrol officers to remember to don or change their gloves before handling evidence. If a suspect attempts to flee and should the officer pursue and apprehend the suspect, and during the overcoming of resistance a gun falls from the waist of the suspect, the officer must don or change gloves before retrieving the gun as evidence. If not, the defense can claim the DNA found on the gun was transferred to the gun by the officer after having physical contact with the suspect; and they would be correct. It is important to know that the majority of DNA that is deposited by law enforcement personnel in the crime scene comes from the mouth and nose. That is why it is essential to wear an N-95 mask when entering the crime scene or when inspecting or processing items of evidence.

Unintended destruction

Medical and fire department personnel responding to the scene of a crime can, unwittingly, cause tremendous destruction to the crime scene. Medical and fire personnel rate nothing more than the highest praise for their often-heroic efforts to save lives and to prevent further destruction of buildings and additional loss of life. Granted if your crime scene is on fire, it is most desirable to let the fire department do what they do best; also granted that it is far more important to save a life than it is to preserve evidence. However, most often these departments find themselves involved in incidents that do not involve fires or are bereft the imminent loss of life. It is during these occasions that the crime scene technician wishes most that these departments could balance their responsibilities with the urgent need to preserve the crime scene and the evidence it contains. Even simple contributions such as not discarding used latex gloves into the crime scene would go a long way to prevent crime scene contamination. Fire personnel, anxious to remove victim garments in order to affix AED pads, could well serve the crime scene technician by carefully preserving bloodstain evidence, gun powder burns, and bullet and edged weapon defects.

Not many years ago, your author responded to the hospital following a brutal assault with great bodily injury. The victim had been transported to a local hospital before officers arrived at the scene. The victim had been attacked by an unknown assailant from behind. One of the injuries sustained by the victim was a vicious bite to the back. The bite mark, which was not deep enough to draw blood, was a textbook impression and presented a large quantity of saliva. Unfortunately, in the three minutes that it took your author to report to the hospital, medical personnel had already sanitized the wound with rubbing alcohol and rubbed in an antiseptic ointment, thus destroying any DNA evidence that may have remained and making photography difficult owing to the glossiness of the ointment. The case was not prosecuted by the District Attorney's Office as the victim was unable to identify his attacker, as he was attacked from behind, and there were no other witnesses. The victim had sustained a life-changing injury during the assault, a wound to the side of the face that left a deep scar. The only evidence that would have led to the identity of the attacker would have been the DNA from the saliva surrounding the bite mark, which was lost. Had the nurse just applied a small amount of sterile water to a sterile gauze, both of which were readily available, gently rubbed the area of the bite mark, and placed the gauze back into its original packaging prior to applying the rubbing alcohol, the DNA would have been preserved.

Figure \(\PageIndex{1}\): A bite wound that lost its vital evidence. Author's collection