Northern Liberties has gotten safer since it metamorphosed into one of Philadelphia's most popular areas, but the slaying of Sabina Rose O'Donnell just north of the neighborhood's Girard Avenue border was a sharp reminder that trendy, transitional areas often begin to expand into poor, crime-ridden ones. But anyone looking for logic about O'Donnell's death shouldn't look at the changing face of Northern Liberties, says one expert. "Gentrification often tends to reduce crime, rather than increase it," said David Elesh, a Temple sociologist.