A 35-year-old man is brought to the emergency department with a gunshot wound to the chest. The entry wound is small and circular, but the exit wound is large and irregular. Which investigation is most appropriate to determine the distance from which the firearm was discharged?

## Investigation of Choice for Firearm Distance Determination ### Powder Residue Analysis and Tattooing Pattern **Key Point:** The distance from which a firearm is discharged is determined by examining powder residue (stippling/tattooing) around the entry wound. This is the gold standard forensic investigation for distance estimation. ### Distance Categories Based on Powder Residue | Distance Range | Powder Pattern | Characteristics | Forensic Finding | |---|---|---|---| | Contact/Close range (< 15 cm) | Soot + stippling | Black discoloration + small abrasions | Soot and powder particles present | | Intermediate range (15 cm–1 m) | Stippling only | Tattooing without soot | Powder grains without soot | | Distant range (> 1 m) | No stippling | Smooth entry wound | Absence of powder residue | **High-Yield:** Tattooing (stippling) is caused by unburned and partially burned powder grains striking the skin. It cannot be wiped away (unlike soot) and is therefore pathognomonic for intermediate-range firing. **Clinical Pearl:** The absence of powder residue does NOT mean the weapon was fired from a distance >1 m — some firearms produce minimal residue. Conversely, presence of residue confirms firing from <1 m distance. ### Why This Investigation is Superior 1. **Specific:** Powder residue patterns are unique to firearm discharge and cannot be produced by other mechanisms. 2. **Quantifiable:** The density and distribution of stippling can be mapped and measured. 3. **Preserved:** Tattooing marks are permanent on tissue and can be documented photographically. 4. **Admissible:** Accepted in all forensic and legal proceedings. **Mnemonic:** **SOOT-TING** = **S**oot (contact), **O**nly stippling (intermediate), **O**ver 1 meter (distant), **T**attooing pattern, **I**ntermediate range, **N**o residue (far), **G**un distance. ### Supporting Investigations - **Photographic documentation:** Entry and exit wounds photographed with scale. - **Wound trajectory analysis:** Using probes or imaging to determine firing angle. - **Neutron activation analysis (NAA):** Detects trace metals (lead, barium, antimony) from primer residue on the victim's hands or clothing.