Biological Evidence
Biological evidence includes any material of biological origin: blood, semen, saliva, hair, skin cells (touch DNA), bone, teeth, and body fluids. Blood evidence provides rich information—its pattern (spatters, drips, transfers, pools) can reconstruct the mechanism of injury and victim/assailant positions. Presumptive tests like luminol detect trace blood invisible to the naked eye by producing chemiluminescence when it reacts with the iron in hemoglobin—even after cleaning. DNA extracted from biological evidence can identify individuals with statistical certainties exceeding one in a trillion. Hair evidence can be analyzed microscopically (species, body area, growth phase, damage) or through mitochondrial DNA when nuclear DNA is insufficient.