In the decision by the federal judge who found New York City’s stop-and-frisk policies unconstitutional, one name appears more than any other: that of Jeffrey Fagan, a professor at Columbia Law School and the Mailman School of Public Health.

Fagan, an expert witness for the plaintiffs, analyzed nine years of New York Police Department data that the plaintiffs used to demonstrate that the stop-and-frisk program was riddled with constitutional violations.