DNA on a Fast Food Cup: The Brittany Martinez Case | The FBI Files | S4 E4

An after-school bike ride. A missing 11-year-old. And a lead that didn’t look like a lead at all. In Elgin, Illinois, a frantic search for Brittany Martinez spirals through conflicting alibis, a returned bicycle in the basement, and an eerie “vision” about a creek and farmhouses. As false trails fall away, FBI agents turn to forensics: a single nylon fiber inside her jeans, an inconclusive bite mark, and a stained fast-food cup pulled from a cluttered back seat. Then the river discovery changes everything. Follow The FBI Files as investigators piece together Brittany’s final hours using trace evidence, DNA analysis, and relentless legwork. Was a registered offender the key, or did the truth hide much closer to home? And how did one everyday object tip the balance in court? Watch to see how meticulous evidence, not rumors, exposed what really happened—and why one family would never be the same. Full story inside The FBI Files. #TheFBIFiles #TrueCrime #ForensicScience #DNAEvidence #MissingChildren #FBI #ElginIllinois