Types of Physical Evidence in Criminal Law

Physical Evidence

• Physical evidence can be categorized into three types: fruits of a crime, instrumentalities of a crime, and contraband.
• Fruits of a crime are objects obtained by the defendant as a result of committing the crime, such as money stolen by a bank robber.
• Instrumentalities of a crime are items used by the defendant to commit the crime, such as a crowbar used by a burglar to gain entry into a building.
• Contraband is any property that is illegal for a person to possess, such as child pornography found on a computer.

Documentary Evidence

• Documentary evidence is anything written or printed that is offered to prove or disprove facts pertaining to a case.
• Examples of documentary evidence include bank records, medical records, and certified copies of driving histories.

Admissibility of Evidence

• Admissibility of evidence refers to the legal requirements that must be met before a jury can see or hear about the evidence.
• The evidence must be deemed relevant and reliable, and the court must receive it.
• Admissibility of evidence protects the defendant's constitutional rights, guards the jurors from being misled or confused, and can expedite a trial.
• The officer must obtain the evidence legally and preserve it properly.
• The evidence must be relevant to the case and cannot be unfairly prejudicial, confusing, or based on hearsay.

Crime Scene Investigation

• Recognizing threats to the evidence will determine the appropriate method of protection.
• Different crime scenes may require different methods of protecting the evidence.
• In outdoor crime scenes involving degradable, easily destroyed, biological, or trace evidence, protect the evidence from weather elements.
• Instruct people to move behind the crime scene tape, advising that refusal may result in arrest.

Securing and Protecting a Crime Scene

• The primary officer or investigator will designate a point of entry and exit and assign an officer to maintain a crime scene log at that location.
• Determine if the location is public or private property.
• A person occupying private property has an expectation of privacy that no one can violate without a search warrant or a valid exception to the warrant requirement.

Questioning Witnesses at a Crime Scene

• Identify who to question at a crime scene, including victims, complainants, and witnesses.
• Separate involved people to prevent them from coordinating their accounts of what happened.
• Place people in separate locations, near the crime scene area, but in a place that poses no risk of contaminating evidence.
• Document the names, dates of birth, genders, races, addresses, and telephone numbers of all people involved.

Documenting a Crime Scene

• Use proper lighting to ensure that photographs are neither too dark nor too light to see details.
• Avoid including bystanders, other officers, equipment, or pets in crime scene photographs.
• Photographing perishable, transitory, or fragile evidence ensures its documentation and preservation.
• Examples of perishable evidence include blood, footprints, and tire impressions, or trace evidence, such as hair or fibers.

Impression Evidence

• Footprints, shoe impressions, and tire impressions at the scene 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 bite marks as soon as possible with a scale or identifier.

Fingerprints

• Consider all objects at a crime scene as possible sources of fingerprints.
• Patent prints are visible prints formed from the friction ridges or corrugated lines on fingers.
• Plastic prints are molded or embedded fingerprints created by touching an impressionable surface.
• Latent prints are invisible to the naked eye, but result from body residues left behind when the friction ridges of the hands or feet make contact with a surface.

Crime Scene Investigations

• The good-faith exception doctrine allows evidence to be admissible in court even if the search warrant is later found to have a legal error, as long as the officer executing the warrant believed it was valid.
• Privileged communications are protected from disclosure, including interactions between a sexual assault counselor and a sexual assault victim, and a domestic violence advocate and a domestic violence victim.

Securing and Protecting the Crime Scene

• The purpose of an investigation is to determine what happened, identify and locate the suspect, and develop evidence to establish probable cause for an arrest.
• The preliminary investigation focuses on establishing whether a criminal act has been committed and, if so, what type, when, and where it was committed.

Documenting the Crime Scene

• Photographs should be taken to ensure that they are in focus and have proper lighting to avoid glare and flashback.
• Use a flashlight or vehicle spotlight for enhanced lighting, and consider flood lighting for overall pictures.
• Photographic framing is important to depict what you are trying to document, and avoid including bystanders, officers, equipment, or pets in crime scene photographs.
• Use a camera with a flash, and avoid using a personal cell phone camera or agency-issued cell phone camera.

Photographing Evidence

• Perishable, transitory, or fragile evidence should be photographed to ensure its documentation and preservation.
• Examples of perishable evidence include blood, footprints, and tire impressions, or trace evidence like hair or fibers.
• Transitory evidence is evidence that can blow or wash away.

Collecting and Packaging Evidence

• Change gloves between collecting each piece of evidence needing DNA analysis to prevent cross-contamination.
• Use proper tools, equipment, containers, and packaging to prevent contamination and degradation of evidence.
• Place each piece of evidence collected for DNA analysis in its own, separate container.
• Use breathable containers like paper bags for wet evidence, and avoid packaging wet items improperly.

Trace Evidence

• Trace evidence is small quantities of material transferred from a victim or suspect to each other or to a crime scene.
• Examples of trace evidence include human hair, animal hair, textile fibers, rope, feathers, soil, glass, and building materials.
• Microanalysis is the process of analyzing trace evidence with a microscope to determine a possible source or origin.

Chemical and Toxicological Evidence

• Identify controlled substances and drug paraphernalia by sight or odor, and use field test kits to test substances before collecting and packaging them as evidence.
• Package sharp objects like needles or syringes in puncture-proof packages clearly labeled with "WARNING: SHARPS."
• Use PPE when encountering chemical or biological substances.
• Be aware of hazardous substances like fentanyl or carfentanil, which can be absorbed through mucous membranes.

Photo Array Presentations

• Number all photographs and filler photographs used in the array before presenting the array to the victim or eyewitness.
• Simultaneous presentation occurs when the independent administrator presents a group of photographs to the victim or eyewitness all at once.
• Sequential presentation occurs when an independent administrator presents individual photographs to the victim or eyewitness one at a time.
• Agency policies and procedures will specify which method is authorized.