Sherlock in Real life: How homicide detectives process a domestic crime scene

[Soz]

Over 20% of murders happen at home...  at the victim's residence. In the critical first 24 hours of a homicide investigation, the bathroom of a murder victim is a focal point for homicide detectives and forensic investigators due to its potential to yield a wealth of probative evidence.  Homicide detectives in fact treat the bathroom as a high-priority area, systematically collecting biological evidence (blood, DNA, fluids), latent prints, trace evidence, and physical items while documenting the scene meticulously. By integrating forensic techniques like presumptive tests, ALS, and fingerprint enhancement with scene reconstruction and coroner collaboration, investigators maximize evidence recovery to identify suspects, establish timelines, and reconstruct the crime. 

Bathrooms are often intimate, confined spaces where perpetrators may leave behind biological, trace, or physical evidence, either inadvertently or during attempts to clean up or stage the scene.

This methodical approach ensures the bathroom’s evidentiary value is fully leveraged before degradation.

 I was chatting with a friend who is MPD in Minneapolis and below is what homicide detectives prioritize in a bathroom during this initial period, grounded in forensic science principles and investigative techniques:

1. Securing and Documenting the SceneUpon arrival, detectives and crime scene investigators (CSIs) prioritize securing the bathroom to prevent contamination, cordoning off the area and limiting access to authorized personnel only. The initial walkthrough involves a meticulous survey to identify the “focal point” of the crime—often the location of the victim’s body or the primary area of disturbance, such as a bloodstained sink or bathtub. Detectives document the scene comprehensively using:

• Photography: High-resolution photographs capture the bathroom’s overall layout, including fixtures (sink, toilet, shower), bloodstains, and items out of place (e.g., a displaced towel or overturned toiletries). Close-up shots focus on specific evidence like fingerprints or droplets.
• Sketches: Detailed sketches, often from an overhead perspective, map the positions of the victim, evidence, and fixtures, with precise measurements (e.g., “blood smear 12 inches from the sink’s edge”). These complement photographs by providing spatial context.
• Notes: Investigators record observations, such as water in the sink, wet towels, or signs of a struggle (e.g., a cracked mirror), to preserve initial impressions and guide evidence collection.

This documentation ensures the scene’s integrity and provides a reference for later analysis, as once evidence is moved, it cannot be restored to its original state.2. Biological Evidence CollectionBathrooms are rich in biological evidence due to their association with bodily fluids and personal hygiene. Detectives prioritize:

• Blood Evidence: Bloodstains, splashes, or pools are critical for reconstructing the crime and identifying individuals. Investigators look for:
  • Spatter Patterns: High-velocity spatter (e.g., from a gunshot) or cast-off patterns (from a weapon) on walls, tiles, or mirrors can indicate the attack’s nature and position. For example, a blood trail from the sink to the drain suggests cleanup attempts.
  • Presumptive Tests: CSIs use catalytic tests (e.g., Kastle-Meyer or luminol) to confirm suspected bloodstains, distinguishing them from substances like rust or ketchup. Luminol detects trace blood invisible to the naked eye, such as in drains or tile grout.
  • DNA Collection: Blood, saliva, or skin cells (e.g., under the victim’s fingernails) are swabbed for DNA analysis. For instance, blood in the sink may belong to the perpetrator if they washed their hands. Swabs are taken with sterile tools, and a substrate control sample (from an adjacent clean area) is collected to rule out contamination.
• Other Bodily Fluids: Semen, saliva, or sweat may be present, especially in cases involving sexual assault or close-contact violence. An alternate light source (ALS) is used to detect these fluids, which fluoresce under specific wavelengths. For example, saliva on a toothbrush or semen on a towel could link a suspect to the scene.

3. Latent Prints and Touch EvidenceBathrooms often have smooth, non-porous surfaces (e.g., glass, ceramic tiles, metal faucets) ideal for recovering latent fingerprints or palm prints. Detectives focus on:

• Fingerprint Collection: CSIs dust surfaces like the sink, mirror, or door handles with magnetic powder to reveal latent prints. Blood-stained prints, common in violent crimes, may require chemical enhancement (e.g., amido black) for clarity. For example, a bloody fingerprint on a faucet could indicate the perpetrator washed their hands.
• Touch DNA: Surfaces touched by the perpetrator (e.g., a light switch or soap dispenser) are swabbed for trace DNA. This is particularly valuable in bathrooms, where perpetrators may interact with multiple surfaces.

4. Trace EvidenceTrace evidence, such as hairs, fibers, or soil, can link a suspect to the scene or victim. Detectives examine:

• Hairs and Fibers: Hairs in the drain or on a towel may belong to the victim or perpetrator. Fibers from clothing (e.g., a suspect’s jacket caught on a towel rack) are collected using tweezers or tape lifts and sent for microscopic analysis.
• Foreign Substances: Soil or vegetation tracked into the bathroom (e.g., on the floor or in shoeprints) can indicate the suspect’s movements. For instance, soil from an outdoor secondary scene found in the bathroom suggests the perpetrator entered after the crime.
• Chemical Residues: Cleaning products or bleach residues in the sink or bathtub may indicate a cleanup attempt. These are sampled for toxicological analysis to confirm their nature.

5. Physical Evidence and Scene ReconstructionPhysical evidence in the bathroom helps reconstruct the sequence of events. The Amanda Knox - Meredith Kercher trial study and forensic issues surrounding that is my go resource for analyzing all recontructive evidence. Detectives look for:

• Weapons or Tools: A knife, razor, or blunt object (e.g., a heavy soap dish) may be the murder weapon or bear tool marks. These are photographed in place, tagged, and sent for ballistic or microscopic analysis.
• Shoeprints or Impressions: Bloody shoeprints on the floor or bathmat can reveal the perpetrator’s movements. Dental stone casts are made to preserve tread patterns for comparison with suspect footwear.
• Signs of a Struggle: Disrupted items (e.g., a knocked-over shampoo bottle, broken shower rod) or defensive wounds on the victim (visible during the coroner’s examination) indicate a violent encounter. Wet towels or running water suggest a cleanup attempt.

6. Digital and Contextual EvidenceWhile less common in bathrooms, detectives check for:

• Digital Devices: A phone or smart device in the bathroom may contain call logs, texts, or location data relevant to the timeline. These are seized for digital forensic analysis. Not a well-known fact is that some of these forensics experts us Jupyter Notebooks, one recommended a HostJane managed Jupyter computes on AWS to collect and weigh statistical evidence from case files.
• Witness Information: If witnesses report hearing water running or a struggle, detectives prioritize the bathroom for blood or cleaning evidence. For example, an upstairs neighbor’s statement about running water could lead to drain swabs for trace blood.

7. Coroner and Autopsy CoordinationThe medical examiner is notified immediately to assess the body, often in situ if found in the bathroom. Detectives avoid moving the body until the coroner approves, as it may bear evidence like trace fibers or DNA. The coroner’s preliminary examination (e.g., noting lividity or rigor mortis) helps estimate time of death, guiding the investigation timeline. For example, a body in a bathtub with pruning skin suggests prolonged water exposure, refining the time-of-death estimate.8. Time-Sensitive ActionsThe first 24 hours are critical due to evidence degradation:

• Biological Evidence: Blood and fluids degrade quickly, especially in a humid bathroom. Rapid collection and refrigeration are essential.
• Trace Evidence: Hairs or fibers can be lost to air currents or cleaning. Priority collection prevents loss.
• Proactive Analysis: Expedited forensic tests (e.g., DNA or fingerprint searches via CODIS or IAFIS) can generate leads within hours, as seen in cases where rapid DNA matches identified suspects.

[Cole Wyeth]

RE investigations of domestic crime scenes: 

Interesting to know, though it seems this analysis requires specialized equipment, so I can't glean any potential entries to the list?

-Cole