High-Tech, High-Risk Forensics

SAN FRANCISCO — WHEN the police arrived last November at the ransacked mansion of the millionaire investor Raveesh Kumra, outside of San Jose, Calif., they found Mr. Kumra had been blindfolded, tied and gagged. The robbers took cash, rare coins and ultimately Mr. Kumra’s life; he died at the scene, suffocated by the packaging tape used to stifle his screams. A forensics team found DNA on his fingernails that belonged to an unknown person, presumably one of the assailants. The sample was put into a DNA database and turned up a “hit” — a local man by the name of Lukis Anderson.

Bingo. Mr. Anderson was arrested and charged with murder.

There was one small problem: the 26-year-old Mr. Anderson couldn’t have been the culprit. During the night in question, he was at the Santa Clara Valley Medical Center, suffering from severe intoxication.

Yet he spent more than five months in jail with a possible death sentence hanging over his head. Once presented with Mr. Anderson’s hospital records, prosecutors struggled to figure out how an innocent man’s DNA could have...