Using computer code he wrote, he searches his archive for statistical anomalies among the more ordinary murders resulting from lovers’ triangles, gang fights, robberies, or brawls.

The algorithm forms the basis of the Murder Accountability Project (MAP), a nonprofit that consists of Hargrove—who is retired—a database, a Web site, and a board of nine members, who include former detectives, homicide scholars, and a forensic psychiatrist.

By a process of data aggregating, the algorithm gathers killings that are related by method, place, and time, and by the victim’s sex.

Statistically, a town with a serial killer in its midst looks lawless.

“I left messages for months,” he said.

Four years later, the police in Hammond, a town next to Gary, got a call about a disturbance at a Motel 6, where they found a dead woman in a bathtub.

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