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These tasks include:. When an investigator arrives at a crime scene, the need to protect that crime scene becomes a requirement as soon as it has been determined that the criminal event has become an inactive event and the investigator has switched to a strategic investigative response.

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As you will recall from the Response Transition Matrix, it is sometimes the case that investigators arrive at an active event in tactical investigative response mode. In these cases their first priority is to protect the life and safety of people, the need to protect the crime scene and its related evidence is a secondary concern.

This is not to say that investigators attending in tactical investigative response mode should totally ignore evidence, or should be careless with evidence if they can protect it; however, if evidence cannot be protected during the tactical investigative response mode, the court will accept this as a reality. As soon as the event transitions to an inactive event with a strategic investigative response, the expectations of the court, regarding the protection of the crime scene and the evidence, will change.

This change means that there is an immediate requirement for the investigator to take control of and lock down that crime scene. Very often, when the change to strategic investigative response is recognized, first responders and witnesses, victims, or the arrested suspect may still be inside the crime scene at the conclusion of the active event.

All these people have been involved in activities at the crime scene up to this point in time, and those activities could have contaminated the crime scene in various ways. Locking down the crime scene means that all ongoing activities inside the crime scene must stop, and everyone must leave the crime scene to a location some distance from the crime scene area. Once everyone has been removed from the crime scene, a physical barrier, usually police tape, is placed around the outside edges of the crime scene.

Defining of the edges of the crime scene with tape is known as establishing a crime scene perimeter. This process of isolating the crime scene inside a perimeter is known as locking down the crime scene. The crime scene perimeter defines the size of the crime scene, and it is up to the investigator to decide how big the crime scene needs to be.

The size of a crime scene is usually defined by the area where the criminal acts have taken place. This includes all areas where the suspect has had any interaction or activity within that scene, including points of entry and points of exit. The perimeter is also defined by areas where the interaction between the suspect and a victim took place.

In some cases, where there is extended interaction between a suspect and a victim over time and that activity has happened over a distance or in several areas, the investigator may need to identify one large crime scene, or several smaller crime scene areas to set crime scene perimeters. Considering the three stages of originating evidence, an investigator may find that pre-crime or post-crime activity requires the crime scene perimeter to surround a larger area, or there maybe even be an additional separate crime scene that needs to be considered.

For some crime scenes where there are natural barriers, such as buildings with doorways, it is easy to create a crime scene perimeter defining access. This becomes more complicated in outdoor venues or large indoor public venues, where fencing and barricades may be needed along with tape markers to define the perimeters. Once the crime scene perimeter has been established and lock down has taken place, it becomes necessary to ensure that no unauthorized persons cross that perimeter.

Typically, and ideally, there will only be one controlled access point to the crime scene, and that point will be at the entry point for the path of contamination. It is not possible to eliminate all potential contamination of a crime scene. We can only control and record ongoing contamination with a goal to avoid damaging the forensic integrity of the crime scene and the exhibits. Once a crime scene has been cleared of victims, witnesses, suspects, first responders, and investigators, it is necessary to record, in notes or a statement from each person, what contamination they have caused to the scene.

The information being gathered will document what evidence has been moved, what evidence has been handled, and by whom. With this information, the investigator can establish a baseline or status of existing contamination in the crime scene.

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If something has been moved or handled in a manner that has contaminated that item before the lock down, it may still be possible to get an acceptable analysis of that item if the contamination can be explained and quantified. As an example, sometimes in cases of serious assaults or even murders, paramedics have been present at the scene treating injured persons.

When this treatment is happening, non-suspect-related DNA transfer between persons and exhibits can occur. Determining those possibilities is one of the first steps in establishing the level of existing contamination at the time of lock down. With everyone now outside the crime scene and the perimeter locked down, the next step is to establish a designated pathway where authorized personnel can re-enter the crime scene to conduct their investigative duties.

This pathway is known as a path of contamination and it is established by the first investigator to re-enter the crime scene after it has been locked down. Prior to re-entering, this first investigator will take a photograph showing the proposed area where the path of contamination will extend, and then, dressed in the sterile crime scene apparel, the investigator will enter and mark the floor with tape to designate the pathway that others must follow.

In creating this pathway, the first investigator will avoid placing the pathway in a location where it will interfere with apparently existing evidence and will place it only where it is required to gain a physical view of the entire crime scene.


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As other investigators and forensic specialists enter the crime scene to perform their duties, they will stay within the path of contamination and, when they leave the path to perform a specific duty of investigation or examination, they will record their departure from the path and will be prepared to demonstrate their departure from the pathway and explain any new contamination caused by them, such as dusting for fingerprints or taking exhibits. At the same time the crime scene is being defined with perimeter tape, it is also necessary to establish a security system that will ensure that no unauthorized person s enters the crime scene and causes contamination.

For this purpose, a crime scene security officer is assigned to regulate the coming and going of persons from that crime scene. For the assigned security officer, this becomes a dedicated duty of guarding the crime scene and only allowing access to persons who have authorized investigative duties inside the crime scene. These persons might include:. Any unauthorized person who enters or attempts to enter a crime scene should be challenged by the crime scene security officer, and, if that person refuses to leave, they can be arrested, removed from the scene, and charged for obstructing a police officer.

The assigned security officer is responsible for creating and maintaining the Crime Security Log, which can take various forms. Whatever the scale or format, the security log records who attended the scene, when they attended, why they were there, and when they left the scene. An example of a crime scene security log is shown in the following example.

As we have already learned in the STAIR tool, analysis is the process that must occur to establish connections between the victims, witnesses, and suspects in relation to the criminal event. The crime scene is often a nexus of those events and consequently, it requires a systematic approach to ensure that the evidence gathered will be acceptable in court.

Exhibits, such as blood, hair, fiber, fingerprints, and other objects requiring forensic analysis, may illustrate spatial relationships through evidence transfers. Other types of physical evidence may establish timelines and circumstantial indications of motive, opportunity, or means.

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All evidence within the physical environment of the crime scene is critically important to the investigative process. At any crime scene, the two greatest challenges to the physical evidence are contamination and loss of continuity. Contamination is the unwanted alteration of evidence that could affect the integrity of the original exhibit or the crime scene. This unwanted alteration of evidence can wipe away original evidence transfer, dilute a sample, or deposit misleading new materials onto an exhibit.

Just as evidence transfer between a suspect and the crime scene or the suspect and the victim can establish a circumstantial connection, contamination can compromise the analysis of the original evidence transfer to the extent that the court may not accept the analysis and the inference that the analysis might otherwise have shown.

Contamination is a fact of life for investigators, and any crime scene will have some level of contamination before the scene becomes an inactive event and the police can lock down the location. While issues of life and safety are at risk, the court will accept that some contamination is outside the control of the investigator. That tolerance for controlling contamination changes significantly once the crime scene is locked down and is under control.

Once the scene has been locked down, crime scene management procedures must be put in place. Crime scene contamination presents three challenges for investigators, namely:. This practice of identifying and recording the known contamination is necessary, and even if contamination has taken place, identifying and explaining that contamination may salvage the analysis of exhibits that have been contaminated. During the critical period between the lockdown of the crime scene and obtaining a warrant to search the crime scene, investigators need to consider the possibilities for ongoing contamination.

If reasonable grounds exist to believe that evidence of the crime will be damaged or destroyed by some threat of contamination, the investigator has the authority, under exigent circumstances, to re-enter that crime scene without a warrant to take the necessary steps to stop or prevent contamination and protect the evidence. The very act of entering the crime scene to collect evidence, and the process of evidence collection, are forms of contamination. The goal in controlling ongoing contamination is to avoid damaging the forensic integrity of the crime scene and its associated exhibits.

It is this goal that makes crime scene management procedures essential to the investigative process. Like controlling contamination, establishing and maintaining continuity of evidence are protocols that protect the integrity of that evidence. For any evidence to be accepted by the court, the judge must be satisfied that the exhibit presented is the same item that was taken from the crime scene. The evidence to show continuity will come from the investigator testifying that the exhibit being presented is the same exhibit that was seized at the crime scene.

This testimony is supported by the investigator showing the court their markings on the exhibit or its container. These markings will include the time, date, and investigator initials, as well as a notebook entry showing the time, date, and place when the item was transported and locked away in the main exhibit holding locker. This evidence is further supported by an Exhibit Log that shows the exhibit as part of the crime scene evidence detailing where at the crime scene it was found, by whom it was found, and the supporting initials of anyone else who handled that exhibit from the crime scene continuously to the main exhibit locker.

Any process where that exhibit is removed from the main exhibit locker for examination or analysis must be similarly tracked and documented with the initials, time, and date of any other handlers of the item. Any person who has handled the exhibit must be able to take the stand providing testimony that maintains the chain of continuity of the exhibit. These are simple processes yet critical. If they are not followed rigorously, it can result in the exclusion of exhibits based on lost continuity.

One of the big dilemmas in crime scene management is determining where the criminal event happened or where the event extended to. Making these determinations provides the investigator with the locations where evidence of the crime may be found. This is often not a simple matter of just attending one location or thinking about the criminal event in just a single timeframe.

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In the investigative process, there are three possible stages of time where evidence can originate. These are the pre-crime stage, the criminal event stage, and the post-crime stage. These three stages of crime can also mean there could be other locations outside the immediately crime scene area where criminal activities might have also taken place and evidence might be found.

The point to remember about the originating stages of evidence is that each of these stages provides possibilities for collecting evidence that could connect the suspect to the crime.

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When considering theory development or making an investigative plan, each of these stages of the criminal event should be considered. Evidence does not always appear as a fully formed piece of information that offers an immediate connection or an inference to implicate a suspect.