A disputed paternity case — the child's DNA matches the alleged father at every locus. DNA fingerprinting (STR loci — PCR-amplified; match probability in billions) settles paternity, identifies disaster victims, and convicts from a cigarette butt — buccal swabs, bloodstains, semen all yield profiles. Contamination control and chain of custody make it court-worthy. The double helix is the ultimate witness — it cannot lie, only be mishandled.