Investigations | Section 1.3

Fundamentals of Criminal Investigation by Adam J. McKee

Section 1.3: Preliminary Investigations

One of the most important aspects of securing a crime scene is to preserve the scene with minimal contamination and disturbance of any physical evidence present.  This, as important as it may be, must be a secondary concern. Officer and public safety must be the first priority.

Arrival and Approach

The investigation begins the moment an officer is dispatched to the scene.  The first responding officer should begin by making note of all dispatch information, including the address, time, date, type of call, and any information known about parties involved.  The officer should be alert from the onset, taking care to note any vehicles or persons leaving the vicinity of the crime scene, and those remaining near the crime scene that may be involved.  The actual scene must be approached cautiously. Scan the area thoroughly, noting any possible secondary crime scenes. The officer should make an initial observation of the entire scene, assessing the scene for potential dangers to safety.

Dealing With Exigencies

The initial responding officer must treat each crime scene as a crime in progress until he or she is sure that it is otherwise.  The first priority is always to ensure there are no immediate threats to the officer’s safety and the safety of other responders.  The officer should carefully scan the area for sights, sounds, and smells that may indicate danger to personnel. These can include hazardous materials such as gasoline, anhydrous ammonia, and chemical solvents.  In cases where a safe response is beyond the reach of the responding officer’s agency, an appropriate agency should be contacted immediately. Assistance from another agency is frequently required in cases of clandestine drug laboratories, biological weapons, and radiological or chemical threats.  Do not enter a scene if you have not been trained in proper safety procedures for that kind of scene.

Aside from environmental threats, the perpetrator, accomplices, and other potentially dangerous individuals may be present at the scene.  The environment must be considered hostile until a security sweep has proven otherwise. If the situation requires it, summon and wait for backup to arrive before entering the scene.

Once it has been determined that the scene is safe or has been made so, then other emergencies should be considered.  Emergency medical treatment of those at the scene should be a second priority. Every effort should be made to reduce the risk of scene contamination during the administration of medical assistance.  The officer should guide medical personnel through the scene, pointing out possible physical evidence and instructing them to make minimal contact with it. Remember that bullet holes, knife tears, and so forth in clothing are potential evidence.  Instruct medical personnel to cut around these potentially valuable sources of evidence.  Any potential source of contamination or alteration of the appearance of the scene by emergency medical personnel should be documented.  EMTs will usually move the victim, and this should be noted. They should be asked not to alter the scene in any way, such as by cleaning up.

If medical personnel were the first responders, make sure to note the name, unit, and contact information for all personnel at the scene.  If the victim is removed, make sure to obtain information about where he or she is being taken from emergency medical personnel. If there is a chance that the victim may die, try to obtain a “dying declaration.”  If the victim or the suspect is transported to a hospital, attempt to send an officer with them to document any statements made and to preserve any evidence. If no officers are available, request that the ambulance personnel preserve evidence and document any comments.

Has a Crime Been Committed?

An alleged crime scene should be treated as such until it can be determined otherwise.  This issue should be carefully considered before time and resources are allotted to a potentially unnecessary investigation.

Security and Control

The first responding officer has the challenging task of controlling all individuals at the scene.  Individuals must be prevented from altering or destroying evidence.  This is best accomplished by restricting movement through the scene unless absolutely necessary, such as with emergency medical personnel.  The officer is also responsible for the safety of those at the scene.

The officer must also identify all individuals present at the scene.  All nonessential personnel should be excluded from the scene.  This includes officers not working the case, politicians, and the media.  Bystanders should be removed from the scene, but only after determining that they are not witnesses.  Victims and the family and friends of the victim must also be controlled, but with tact and compassion.  Witnesses and suspects should both be secured and separated.

Before the scene can be properly protected, it must be identified and boundaries established.  Crime scene perimeters are usually established by working outward from the focal point to include:

  • Where the crime actually occurred
  • Likely points of entry and exit of suspects and witnesses
  • Places where the victim and evidence may have been moved

Where existing boundaries are available, such as walls, doors, and fences, they should be used.  Where no preexisting boundaries exist, they should be established using anything available, from personnel and vehicles to cones and crime scene tape.  Once the boundaries have been established, any person entering or leaving the scene should be documented.

Another early priority is to effect measures designed to protect evidence that may be lost or compromised.  The elements can destroy evidence, as well as the activity of humans and animals. Rain, wind, sun, snow, vehicle traffic, footsteps, can all potentially destroy valuable evidence.

It is important to maintain the integrity of the scene from the very beginning.  Often, contamination of the scene is done by police officers, mostly without thinking about the consequences.  No one within the boundaries of a crime scene should engage in behaviors that alter or modify the scene. Examples are:  Smoking, chewing tobacco, spitting, using telephones and bathrooms, eating, drinking, moving items, adjusting thermostats, opening windows and doors, touching things unnecessarily and without precautions (such as gloves), and littering.

Change of Control

In most jurisdictions, investigators, not the first responder, will investigate the scene of serious crimes.  When turning over control of the scene to investigators, the first responder should:

  • Brief the investigators taking charge
  • Assist in controlling the scene if necessary
  • Turn over documentation such as entry/exit logs
  • Remain at the scene until relieved of duty

An important consideration for the lead investigator is the composition of the crime scene team.  In many cases, a lone investigator can do an adequate job of processing the scene. In others, however, the scope and complexity of the scene may dictate that additional human resources are required.  Additional personnel will often be necessary when there are multiple scenes, multiple victims, or numerous witnesses. Circumstances where forensic evidence dictates the assistance of additional resources often arise.  Keep in mind that the scene must remain secure and entry and exit documentation must still be maintained. Specialized tasks should be performed by persons with expertise in those areas. Even basic tasks such as photography, sketching, print lifting, and evidence collection require specialized skills.  When specific team members are assigned to specific tasks, the lead investigator should document those assignments.

First Responder Documentation

The initial responding officers should carefully document their actions prior to and upon arrival at the scene.  It is critical that these things be documented as quickly as possible after the event such that the information is preserved.  Observations about the scene, such as the location of items and persons within the scene and the appearance of the scene upon arrival should be recorded.  It is also critical to note things that are time-sensitive, such as the temperature, weather, and time of day. Conditions that may have changed or deteriorated with time (such as smells and the presence of ice) should be noted.  Also important are things that have changed or been contaminated by the first responder, such as whether doors were initially open or closed. Personal and contact information from victims, witnesses, and suspects should be recorded, along with any statements or comments they made.  Finally, the initial responding officer should record his or her own actions at the scene, as well as those of others present, such as emergency medical personnel.

Investigator Scene Assessment

Once the scene has been turned over to the investigators (or it has been decided that the initial responder will be conducting the investigation), the investigators must make an initial assessment of the scene.  The first priority will generally be to talk with the first responder regarding his or her observations about the scene. Second, the investigator should verify that the first responder has conducted a protective sweep of the scene, and that it has been properly secured.  Following this, the investigator should survey the scene for environmental hazards, such as the presence of blood that may contain bloodborne pathogens.

Once the scene has been determined to be safe and all medical emergencies have been taken care of, then the exigency exception to the search warrant requirement has ceased to be valid.  Investigators should evaluate the search and seizure issues carefully and determine the necessity of obtaining either consent or a search warrant. Contrary to popular belief, there is no general “crime scene exception” to the search warrant requirement.  When in doubt, obtain a warrant.

Once it is determined that a search of the scene will be lawful, the next order of business is to establish a path of entry and exit to the scene to be used by authorized personnel.  The initial boundaries of the scene should be reevaluated and expanded if necessary.

The investigator will also want to establish a secure area within close proximity to the scene for the purpose of consultation and equipment staging.  In the same or a slightly different area, a temporary evidence storage area should be established. This must be done with consideration of the rules of evidence, with special attention being paid to chain of custody issues.

If there are multiple scenes, then communication must be established between the investigators at all scenes.

During the scene assessment by the investigator, the need for additional investigative resources must be considered.  During this phase of the assessment, consider the need for legal consultation (usually the prosecutor’s office), specialized scientific consultation (such as crime lab requirements and capabilities), and the investigative aid of another agency.  If an investigator realized that he or she lacks the necessary training and equipment to adequately investigate a particular crime, then the assistance of another should immediately be sought.

The investigator must also continue to maintain the integrity of the scene.  The entry and exit of authorized personnel must still be documented, and unauthorized persons must be kept out of the scene.  The area around the scene should be canvassed, and the results should be documented.

Scene Walk-through

Conducting a walk-through provides the investigator with an overview of the entire scene.  This knowledge is necessary to effectively manage the evidence collection process. Fragile and perishable evidence must be collected first.  Evidence that may be compromised must be given first priority for documentation, photographing, and collection.

During this walk-through, the investigator must take care to use the established entry path, taking care to avoid contamination.  Preliminary documentation of the scene should be prepared as the scene is being observed. It is important to document how the scene was found before any evidence is moved or collected.

Contamination Control

After safety, contamination control is one of the most important things for the crime scene investigator to consider.  In fact, these issues are intricately related. Physical, biological, and chemical hazards at the scene threaten the health and safety of the investigator.  Contamination of the evidence by personnel at the scene will generally result in the inability to use evidence in court. Thus, the prevention of contamination is essential for the safety of personnel and the integrity of evidence.  

The easiest culprits to eliminate are nonessential personnel.  As previously indicated, all nonessential personnel must be kept out of the scene.  Those that are essential must follow the established entry and exit routes. When contamination is likely, such as when EMTs have been at the scene, the investigator should consider collecting elimination samples from these individuals.  Elimination samples are samples such as fingerprints and DNA taken those known to have been at the scene and known not to have been involved in the crime, such as victims, investigators, and emergency medical personnel.

The use of personal protective equipment (PPE) is essential to the prevention of contamination of both the scene and personnel at the scene.  PPE consists of a wide variety of equipment designed to protect the user from hazards in the environment, such as gloves, respirators, and safety goggles.  The use of gloves (usually latex or nitrile) is recommended at every scene. Gloves protect the user from hazards in the environment (such as bloodborne pathogens), and protect the integrity of evidence by preventing the transfer of fingerprints and DNA.  It must be remembered that in performing its function, PPE becomes contaminated. Equipment must be sanitized between uses, or else disposed of and replaced. Most experts agree that single-use equipment should be used for the direct collection of biological samples.

Scene Arrival Procedural Summary

  • Note or log dispatch all dispatch information.
  • Be aware of any persons or vehicles leaving the crime scene.
  • Approach the scene cautiously; scan the entire area, thoroughly assessing the scene.
  • Note any possible secondary crime scenes.
  • Be aware of any persons and vehicles in the vicinity that may be related to the crime.
  • Make initial observations (look, listen, smell) to assess the scene and ensure officer safety before proceeding.
  • Remain alert and attentive.
  • Assume the crime is ongoing until determined to be otherwise.
  • Treat the location as a crime scene until assessed and determined to be otherwise.
  • Safely direct additional responding units into the area.

Officer Safety Procedural Summary

  • Ensure that there is no immediate threat to other responders; scan area for sights, sounds, and smells that may present danger to personnel (e.g., hazardous materials such as gasoline, natural gas).
  • If the situation involves a clandestine drug laboratory, biological weapons, or radiological or chemical threats, contact the appropriate personnel or agency prior to entering the scene.
  • Approach the scene in a way calculated to reduce risk of harm to officers while maximizing the safety of victims, witnesses, and others in the area.
  • Survey the scene for dangerous persons and control the situation.
  • Notify supervisory personnel and call for assistance and backup as necessary.

Emergency Care Procedural Summary

  • If victims are present, assess them for signs of life and medical needs and provide immediate medical attention.
  • Call for medical personnel.
  • Guide medical personnel to the victim in a way that minimizes contamination of the crime scene.
  • Point out potential physical evidence to medical personnel, instruct them to minimize contact with such evidence (e.g., ensure that medical personnel preserve all clothing and personal effects without cutting through bullet holes, knife tears), and document movement of persons or items by medical personnel.
  • Instruct medical personnel not to “clean up” the scene and to avoid removal or alteration of items originating from the scene.
  • If medical personnel arrived first, obtain the name, unit, and telephone number of attending personnel, and the name and location of the medical facility where the victim is to be taken.
  • In some instances, fingerprint and shoe impressions of medical personnel may need to be taken for elimination purposes.
  • If there is a chance the victim may die, attempt to obtain “dying declaration.”
  • Document any statements/comments made by victims, suspects, or witnesses at the scene.
  • If the victim or suspect is transported to a medical facility, send a law enforcement official with the victim or suspect to document any comments made and preserve evidence. (If no officers are available to accompany the victim/suspect, stay at the scene and request medical personnel to preserve evidence and document any comments made by the victim or suspect.)
  • Safeguard evidence, such as a weapon, that is taken into custody.
  • Follow chain-of-custody procedures as soon as the evidence is confiscated.

Scene Control Procedural Summary

  • Control all individuals at the scene—prevent individuals from altering or destroying physical evidence by restricting movement.
  • Identify all individuals at the scene.
  • Suspects and witnesses should be separated, and bystanders should be questioned to determine if they are witnesses.
  • Victims, family, and friends need to be controlled, but in a way that shows compassion.
  • Exclude unauthorized and nonessential personnel from the scene (e.g., law enforcement officials not working the case, politicians, media).

Boundary Procedural Summary

  • Establish boundaries of the scene(s), starting at the focal point and extending outward to include Where the crime occurred, potential points and paths of exit and entry of suspects and witnesses, places where the victim or evidence may have been moved (be aware of trace and impression evidence while assessing the scene).
  • Secure the scene.  Set up physical barriers (e.g., ropes, cones, crime scene barrier tape, available vehicles, personnel, other equipment) or use existing boundaries (e.g., doors, walls, gates).
  • Document the entry/exit of all people entering and leaving the scene, once boundaries have been established.
  • Protect the scene.  Control the flow of personnel and animals entering and leaving the scene to maintain integrity of the scene.  Institute measures to preserve/protect evidence that may be lost or compromised (e.g., protect from the elements (rain, snow, wind) and from footsteps, tire tracks, sprinklers).
  • Document the original location of the victim or any objects that you observe being moved.
  • Consider search and seizure issues to determine the necessity of obtaining consent to search and/or obtaining a search warrant.  Remember: There is no crime scene exception to the search warrant requirement.

Chance of Control Procedural Summary

  • Brief the investigator(s) taking charge.
  • Assist in controlling the scene.
  • Turn over responsibility for the documentation of entry/exit.
  • Remain at the scene until relieved of duty.

Documentation Procedural Summary

  • Document observations of the crime scene, including the location of persons and items within the crime scene and the appearance and condition of the scene upon arrival.
  • Document conditions upon arrival (e.g., lights on/off; shades up/down, open/closed; doors and windows open/closed; smells; ice, liquids; movable furniture; weather; temperature; and personal items.)
  • Document personal information from witnesses, victims, suspects and any statements or comments made.
  • Document your own actions and actions of others.

References and Further Reading

Technical Working Group on Crime Scene Investigation. (2000).  Crime Scene Investigation: A Guide for Law Enforcement.  Available:


Modification History

File Created:  05/02/2019

Last Modified:  04/30/2021

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This work is licensed under an Open Educational Resource-Quality Master Source (OER-QMS) License.

Open Education Resource--Quality Master Source License



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