In 2012, when San Diego police used DNA testing to try and solve the 1984 beachside rape and murder of a 14-year-old girl, they came up with two suspects: a convicted rapist who’d died in 2011, and a man who’d worked as a SDPD crime-lab analyst from 1982-2002. Was the analyst guilty ... or had his DNA simply gotten mixed into the evidence sample by mistake? This enthralling Atlantic piece investigates.

Photo of San Diego’s Ocean Beach by John Eckman