The victim lay across the doorway of a filthy Mount Airy home, a 12-gauge shotgun blast through his chest. The suspect had called in a confession, and the evidence was clear. But that day in April 1999, police puzzled over dark stains on a wall far from the man's body.
"It didn't make sense," said forensic investigator Mitchell Dinterman. "These were all the way across the room."
He noticed an open window. The stains, he realized, came from flies.
Crime scene investigators have long relied on their own judgment to distinguish blood spatter from the look-alike stains left by flies that land on the body and then on a spot nearby. Now a biology professor...