A child killer taunted little girls with terrifying notes, Indiana police say. After 30 years, DNA led to an arrest.

The message was slashed onto the weather-beaten planks of a barn in the empty farmland not far from where the girl's body had been found.

Police in northern Indiana stared at the jerky handwritten scrawl in May 1990, realizing this was the most significant clue to drop in the region's most publicized...