Forensic Science: Crime Scene Investigation, Observation, and Legal Applications

Crime Scene Sketching

Crime scene sketches provide an essential visual record depicting the layout of a location and the spatial relationships of evidentiary items. Sketches are categorized into overview sketches (bird's-eye view or floor plan), elevation sketches (showing vertical planes such as bloodstains on walls), and exploded view or cross-projection sketches (combining floor plan and flattened walls to show relative positions of items on them). Preliminary rough sketches created on-scene without precise scaling must be clearly labeled "Not to Scale", whereas final sketches utilize graph paper, rulers, compasses, and precise measuring instruments such as tape measures, surveyor's wheels, laser rangefinders, or a Total Station.

Constructing a sketch begins with drawing the perimeter outline with openings for doors and rectangles for windows, followed by recording perimeter dimensions. Furniture and evidence are added using basic shapes and assigned numbers or letter identifiers. Every sketch must indicate true North, provide a scale and legend, and list header details including date, time, location, and the victim's name (or John Doe / Jane Doe if unidentified). Critical evidence, such as a body, is positioned via triangulation—measuring exact distances from the evidence to two fixed, unmovable points.

Forensic Observation and Memory Processing

Forensic investigators must observe, interpret, and report physical evidence accurately, though human error remains a risk. Effective observation requires a conscious effort: systematically scanning environments using all five senses, observing slowly, connecting findings to prior knowledge, avoiding hasty conclusions, and capturing precise photographic and written documentation. Observations represent direct sensory data gathering, whereas perceptions are subjective interpretations derived from observations. Perceptions can easily be faulty; for instance, assuming a scoop of pink ice cream is strawberry when it is actually pink-colored vanilla demonstrates how cognitive assumptions introduce error.

Information processing follows a structured neural sequence: Sensory Input $\rightarrow$ Attention $\rightarrow$ Perceptions $\rightarrow$ Short-term memory $\rightarrow$ Long-term memory. Sensory information that is not actively attended to or transferred is quickly lost. Short-term memory holds information for only a few seconds unless maintained through active rehearsal before conversion to long-term storage.

Brain Structure and Functional Lobes

The human cerebrum is divided into four primary lobes that process distinct types of cognitive and sensory information necessary for observation and investigation.

The Frontal Lobe governs reasoning, planning, speech production, emotional response, and problem-solving. The Parietal Lobe handles movement, spatial orientation, recognition, and sensory perception of external stimuli. The Occipital Lobe is dedicated exclusively to visual processing. The Temporal Lobe contains the auditory cortex and is responsible for memory formation, perception, and processing speech.

Deductive Reasoning in Forensics

Deductive reasoning is a logical thinking process where an investigator derives specific conclusions from established facts through sequential steps. It involves formulating a hypothesis and evaluating all potential outcomes. For example, combining Premise #1 (a bloody knife is found beside a deceased woman), Premise #2 (the woman suffered fatal stab wounds), and Premise #3 (the blood on the knife matches the victim's DNA) leads to the logical conclusion that the knife was the murder weapon. However, deductive conclusions are vulnerable to error if any underlying premises or assumptions are incorrect.

The Innocence Project and Eyewitness Reliability

Founded in 1992 by Barry Scheck and Peter Neufeld, The Innocence Project seeks to re-examine post-conviction cases and exonerate wrongfully convicted individuals using DNA evidence. The organization has re-evaluated over 360 cases, uncovering wrongful convictions in 87% of those reviewed. Across the United States, DNA testing has led to 575 post-conviction exonerations, including 35 individuals saved from death row. While all 50 states have enacted post-conviction DNA testing laws, access remains restricted due to strict statutory limitations, high testing costs reaching up to $50,000 per case, and the absence of testable biological evidence in many cases.

DNA evidence is critical because eyewitness testimonies are not scientific evidence and frequently contain unintentional errors. Due to the high rate of memory distortion and faulty perceptions among witnesses, the justice system strongly discourages criminal convictions supported solely by eyewitness statements.