These consequences are on full display in “Charged: The New Movement to Transform American Prosecution and End Mass Incarceration,” by Emily Bazelon, a lecturer at Yale Law School and staff writer at The New York Times Magazine. In “Charged,” a persuasive indictment of prosecutorial excess, Bazelon argues that the lawyers who work in the more than 2,000 prosecutors’ offices around the country — conducting investigations, filing criminal charges and trying cases (or, much more commonly, striking plea bargains) — bear much of the responsibility for over-incarceration, conviction of the innocent and other serious problems of the criminal justice system.

Image Emily Bazelon Credit... Nina Subin

“We often think of prosecutors and defense lawyers as points of a triangle on the same plane, with the judge poised above them: equal contest, level playing field, neutral arbiter,” Bazelon writes. But this is a misconception. As the Brooklyn district attorney, Eric Gonzalez, puts it to her: “It’s all about discretion. Do you authorize the arrest, request bail, argue to keep them in jail or let them out, go all out on the charges or take a plea bargain? Prosecutors decide, especially, who gets a second chance.”

To show how prosecutorial power operates in the real world, Bazelon follows two young defendants through the system: Kevin (a pseudonym), a 20-year-old from the Brownsville neighborhood of Brooklyn who is charged with illegal gun possession, and Noura Jackson, a teenager from Memphis who is accused of murdering her mother.

Their cases are very different — one involving a victimless crime, the other the most heinous crime of all — and so are the district attorneys. Kevin’s prosecutor is Gonzalez, an aspiring reformer and the first Latino to serve as Brooklyn’s district attorney, while Noura’s is Amy Weirich, a hard-charging attorney in the traditional law-and-order mold. Bazelon uses these contrasting cases to demonstrate that having the right (or wrong) prosecutor can make a huge difference — between justice tempered with mercy and grave injustice.

Bazelon tells the tales of Noura and Kevin in rich, novelistic prose, which at its best puts one in mind of Adrian Nicole LeBlanc’s book “Random Family” (2003), about a troubled family from the Bronx in the grip of the criminal justice system. Consider the opening to Noura’s story, the most gripping section of “Charged”: “The blood was everywhere. Spattered on the floor of the hallway, on the doorframe of the bedroom and on the bedposts. Soaked into the sheets and pillows, and covering the body splayed on the floor at the foot of the bed. Jennifer Jackson was naked. Her face was covered by a wastepaper basket. Her chest and torso and hands were slashed, the pale skin torn by the blade of a knife. She’d been stabbed a total of 50 times.”