Crime Scene Investigation Fundamentals

Crime Scene Investigation

• Ensure the crime occurred within your jurisdiction before conducting an investigation.
• Secure the crime scene and look for sources of information and evidence.
• Determine if the crime scene is life-threatening or threatening to officer safety.

Determining the Crime Scene

• The size of the crime scene depends on the type of crime, evidence, and location of evidence.
• Use personal observations and statements from victims and witnesses to determine the extent of the scene.
• Crime scene perimeters should be larger rather than smaller to keep crowds away from evidence.

Securing the Crime Scene

• Attempt to locate and identify the point of the suspect's entry and exit from the crime scene.
• Identify the pieces of evidence farthest from the center of the crime scene.
• Establish boundaries for the crime scene and guard against unnecessary entrance by blocking off the area with crime scene tape.
• Determine a single access point for authorized personnel.

Protecting a Crime Scene

• Do not allow unauthorized removal or alteration of any evidence.
• Protect the scene until it can be photographed and documented.
• Ask the victim or complainant to name potential witnesses and their roles.

Identifying Witnesses

• Separate involved people, including victims, complainants, and witnesses.
• Keep them from discussing the incident with each other until interviews are complete.
• Place people in separate locations, away from the crime scene, to maintain the integrity of their statements.

Photographing Evidence

• Photograph specific items, such as blood drops, weapons, or tire marks, with a scale or identifier.
• Place the scale or identifier close to the item to avoid creating optical illusions.
• Use a scale or identifier to document the extent of injuries on people.

Initiating a Follow-up Investigation

• Review the preliminary report to identify investigative leads.
• Contact witnesses, victims, and potential suspects.
• Review evidence and locate additional evidence.
• Write a capias request, probable cause affidavit, or arrest warrant.

Analyzing Incident Reports

• Review the records of the initial investigation and establish a case file.
• Compare the list of victims, witnesses, and suspects with the case information.
• Review listed evidence and determine if evidence needs further processing or examination.

Identifying Leads

• Identify witnesses who were not available for an interview at the time of the incident.
• Identify collected evidence that needs further processing or examination.
• Conduct a criminal history check to determine if the suspect has fingerprints on file.

Following Leads

• Leads come from various sources, such as anonymous tips, confidential sources, social media, and forensic analysis.
• Always use plain, professional language when following leads.
• Avoid using slang, police jargon, and unprofessional language.

Testifying in Court

• Use proper language and titles, such as "your Honor," "ma'am," and "sir."
• Face the judge while responding to the judge's questions and face the jury when responding to the prosecutor or defense attorney.
• Avoid displaying personal interest in the case and maintain a professional demeanor.
• Provide accurate and complete testimony of the available facts, not to steer the case.

Direct and Indirect Evidence

• Direct evidence: admission by the driver that they were speeding, speed measurement device results, and testimony from eyewitnesses who saw the driver speeding
• Indirect or circumstantial evidence: requires an inference or presumption to establish a fact rather than personal knowledge or observation, e.g. eyewitness testimony that the defendant entered the victim's home around the time of the crime

Types of Evidence

• Testimonial evidence: a witness statement that tends to prove or disprove facts about the case, includes testimonies of law enforcement officers, experts, and other witnesses
• Physical or real evidence: actual objects offered to prove or disprove facts about a case, e.g. trace evidence, biological and touch DNA evidence, impression evidence, firearms evidence, electronic evidence, chemical, or toxicological evidence, and questioned documents evidence
• Documentary evidence: written or recorded information that supports a fact or claim

Collecting and Preserving Physical Evidence

• Correctly identify, protect, collect, preserve, transport, and analyze physical evidence to reduce the likelihood of delivering false results
• Recognize threats to the evidence and determine the appropriate method of protection, e.g. protecting evidence from weather elements in outdoor crime scenes
• Process physical evidence in a separate lesson

Securing a Crime Scene

• Determine how to position authorized personnel, crime scene tape, and natural barriers
• Instruct people to move behind the crime scene tape, advising that refusal may result in arrest
• Determine if the location is public or private property and establish legal authority to secure and protect the crime scene

Separating Victims, Witnesses, and Suspects

• Designate a point of entry and exit and assign an officer to maintain a crime scene log
• Prevent witnesses from influencing each other's statements and separate family members if necessary
• Be empathetic when assessing whether separating family members is necessary, e.g. in child abuse incidents

Providing First Aid and Documenting Evidence

• Responding officers may have to provide emergency first aid and ask fundamental questions about the injury
• Document photographs or sketches of a crime scene and evidence on a person

Searching for and Recognizing Evidence

• Search for evidence based on the type of crime committed, e.g. pry marks on a doorframe or broken windows at a burglary scene
• Use a systematic approach or pattern, such as the grid or spiral search pattern
• Look for evidence of illegal entry, footprints, shoe impressions, tire impressions, and bite marks

Impression Evidence

• Footprints, shoe impressions, and tire impressions can link a suspect to a crime when they match an object in the suspect's possession
• Teeth can provide dental evidence in the form of bite mark impressions that can lead to the identity of the suspect
• Photograph and cast impressions, such as shoe or tire impressions, to preserve them as evidence

Fingerprints

• Consider all objects at a crime scene as possible sources of fingerprints
• Patent prints: visible fingerprints formed from friction ridges or corrugated lines on fingers
• Plastic prints: molded or embedded fingerprints created by touching an impressionable surface
• Latent prints: invisible fingerprints resulting from body residues left behind when friction ridges make contact with a surface, can be identified by crime lab analysis