Evidence Management
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. 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 of Evidence
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 can take place in any number of ways including:
• Police or other first responders interfering with evidence during a tactical investigative
response
• Suspects interfering with the crime scene to cover up or remove evidence
• Victims or witnesses handling evidence
• Animals, including pets, causing unwanted transfer of evidence or even removal of
evidence through contact or consumption
• Weather-related contamination due to rain, wind, or snow diluting or washing away
evidence, or
• Crime scene investigators failing to follow proper crime scene management
procedures and causing contamination of exhibits or cross-contamination between
exhibits during their investigation
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:
1. Preventing contamination when possible,
2. Controlling ongoing contamination, and
3. Recording the known contamination that has taken place
In regards to the phrase “control ongoing contamination”, the word “control” is used because
investigators cannot eliminate ongoing contamination, they can only seek to control it. 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.
Loss of Continuity
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. Evidence must be presented to demonstrate “the chain of continuity”, which tracks
every exhibit from the crime scene to the courtroom.
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.
Attention to Originating Stages of Evidence
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. 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.
When considering theory development or making an investigative plan, each of these stages of
the criminal event should be considered.
1. The Pre-Crime Stage occurs when evidence of preparation or planning can be found
during the investigation. It can include notes, research, drawings, crime supplies or pre-
crime contact with the victim or accomplices. Sometimes items of pre-crime origin, such
as hair and fiber, will be later discovered at the crime scene creating an opportunity to link
the suspect back to the crime
2. The Criminal Event Stage is when the most interaction takes place between the criminal
and the victim, or the criminal and the crime scene. During these interactions, the best
possibilities for evidence transfer occur. Even the most careful criminals have been known
to leave behind some trace of their identity in the form of fingerprints, shoe prints, glove
prints, tire marks, tool impressions, shell casings, hair or fiber, or DNA.
3. The Post-Crime Stage occurs when the suspect is departing the crime scene. When
leaving the crime scene, suspects have been known to cast off items of evidence that can
be recovered and examined to establish their identity. This post-crime period is also the
stage where the suspect becomes concerned with cleaning up the scene. As much as a
suspect may attempt to clean up, evidence transfers from the crime scene are often
overlooked. These can range from hair and fiber on clothing to shards of glass on shoes.
Frequently found post-crime are proceeds of the crime. These are often identifiable articles
of stolen property with unique marks, victim DNA, serial numbers, or sometimes even
trophies that the criminal takes as a keepsake.
Evidence does not always appear as a fully formed piece of information that offers an immediate
connection or an inference to implicate a suspect. It often comes together as fragments of fact in
timelines, spatial relationships, and evidence transfers between the originating stages of evidence
constructing circumstantial pictures to demonstrate the suspect’s identity, the fact pattern of the
crime, opportunity, means, or motive and intent.
Enhancing the Value of Evidence Recovered
Pieces of physical evidence often referred to as exhibits, have investigative values at two
different levels for investigators. At the first level each physical exhibit has a face value
represented by what it is and where it exists within the context of the crime scene. For example a
bloody shoeprint found on the floor of a crime scene tells us that someone transferred evidence
of blood onto their shoe from a source and walked in a particular direction within the crime
scene. These are first level interpretations of evidence that we can reconstruct with our own
observations. At the second level this same bloody shoeprint may be subjected to forensic
examinations that could provide additional information. For example analysis of the shoeprint
pattern, size, and accidental characteristics may allow a positive match to the shoe of a suspect,
or the blood may be examined to match the DNA of a victim or other originating source. Both
these first level and second level values can greatly assist in creating a reconstruction and
interpretation of what happened at the crime scene.
Physical exhibits that need to be examined, seized, and documented at any crime scene are a
major concern for investigators. As mentioned earlier, one of the big challenges for investigators
is to identify and document all of the available evidence and information. This raises the
important questions of what will become evidence and what is going to be important?
When the suspect and the fact-pattern are not immediately apparent, how does an investigator
determine which items within the crime scene need to be considered and taken as possible
evidence? There are some general practices that can be followed, but a guiding principle of
evidence collection followed by most experienced investigators is to err on the side of caution.
More is always better than less. To assist in deciding what could possibly become relevant,
investigators need to consider:
• Items that the suspect may have touched or interacted with
• Items that a victim may have touched or interacted with
• Items that the suspect may have brought to the crime scene
• Items that may have passed between the suspect and the victim
• Items that the suspect may have taken from the crime scene
• Items that the suspect may have discarded while departing the crime scene
Once the crime scene examination has been completed, and the crime scene has been unsecured
and abandoned as an open area, returning to collect forgotten evidence is often not possible. It is
better to collect everything that could possibly be relevant or could become relevant.
In terms of searching for evidence, once the crime scene has been locked down and secured, the
crime scene itself needs to be considered as the first big exhibit. As the first big exhibit, it needs
to be subjected to documentation using photography, video recording, measurements, and
diagrams. Within this first big exhibit, other smaller and possibly-related exhibit may be
discovered. What items are found and where may show spatial relationships of interaction
demonstrating proof to support a sequence of events. This physical evidence will become the
benchmark of known facts that investigators can use to verify the stories of victims and
witnesses, or even the alibi of a possible suspect. Physical evidence at both level-one and level-
two becomes the known facts upon which theories of events may be developed and tested. Any
item could be considered evidence if it demonstrates a spatial relationship relative to the place,
the people, or the times, relative to the criminal event.
The very first step at this point is securing and documenting the crime scene. It is helpful for
investigators to recognize that a crime scene is not just a location where exhibits are found, but
the crime scene should be considered as a single big exhibit unto itself. Not only will individual
exhibits within the crime scene have value as evidence, the spatial relationships between exhibits
in the scene may speak as circumstantial evidence to the overall event.
To secure the crime scene as the first big exhibit, investigators will conduct a complete walk-
through on the path of contamination completely photographing and videotaping the entire crime
scene. This first process is very helpful in demonstrating the exact state of the
