Book excerpt: Andrew Karmen tracks a quarter century of murder in the city Americans have most commonly associated with rampant street crime. Providing both a local and a national context for New York's plunging crime rate, Karmen tests and debunks the many self-serving explanations for the decline. While crediting a more effective police force for its efforts, Karmen also emphasizes the decline of the crack epidemic, skyrocketing incarceration rates, favorable demographic trends, a healthy economy, an influx of hard working and law abiding immigrants, a rise in college enrollment, and an unexpected outbreak of improved behavior by young men growing up in poverty stricken neighborhoods. New York Murder Mystery is the most authoritative study to date of why crime rates rise and fall.