We do not often think of a defense lawyer as someone who wars with her own client, but if it comes to that, Judy Clarke will go to war. Her latest, Dzhokhar Tsarnaev, has admitted responsibility for detonating a bomb among spectators at the 2013 Boston Marathon, killing three people and severely maiming dozens. Federal prosecutors have asked for the death penalty. With Clarke in his corner, it is doubtful that Tsarnaev will ever be put to death for the crime, even if he gets it in his head that he wants to be—that his cause demands martyrdom. Clarke is on a mission bigger than Tsarnaev alone. She is at war with the state—in particular, with the state’s power to impose death. She calls the death penalty “legalized homicide.”

Clarke has taken one notorious death-penalty case after another. There was Ted Kaczynski, the deadly Unabomber, now living out his days in a super-max prison in Colorado, and still furious with his onetime defense attorney (“Judy Clarke is a bitch on wheels and a sicko,” he wrote me); Susan Smith, who strapped her two small boys into car seats and then drove them into a lake and watched them drown; Eric Rudolph, the racist and Christian zealot who set off a bomb in Atlanta during the 1996 Summer Olympics as part of a spree that killed 2 people and injured 150 more; Zacarias Moussaoui, the al-Qaeda operative accused of helping to plan the September 11 attacks; and Jared Lee Loughner, who opened fire in a parking lot near Tucson, Arizona, in 2011, shooting Representative Gabrielle Giffords through the head and killing six others. Her client list is a catalogue of the worst.

You might suspect a lawyer with a record like that to be a publicity seeker, but Clarke is the opposite. She shuns attention. She almost never gives interviews and does not stand before cameras and microphones on courthouse steps. She cultivates invisibility, right down to the muted way she dresses for court appearances. There is a deeper logic at work in her predilection to defend those who have achieved a monstrous notoriety.

In every instance cited above, there is little mystery about the crime itself—and in every case, her clients have been convicted. But while prosecutors have tried to invoke the death penalty, none of her clients have been executed, even when, as with Kaczynski and Rudolph, they are actually proud of what they have done. It’s not unusual for some clients to resist Judy Clarke’s help. One, the white supremacist Buford O. Furrow Jr., who in 1999 walked into a Los Angeles Jewish Community Center and sprayed 70 shots, wounding five, before shooting and killing a mailman an hour later, reportedly threatened to kill her. Clarke defends people who do not wish to be defended, and who don’t have a prayer—clients who are not just dream candidates for the death penalty but who, in some cases, seem determined to embrace it. One case at a time, with whatever legal methods will work, she halts the march toward execution.

Clarke makes her point not with stirring courtroom rhetoric or devastating legal arguments but by a process of relentless accretion, case by case, win by win. This is her cause. Because if the state cannot put these defendants to death, then how can it put anyone to death? Thirty-five executions took place in the United States in 2014 for crimes that form an inventory of human cruelty—and yet few were as willful and egregious as those committed by Judy Clarke’s clients. Meanwhile, Kaczynski is hard at work on his next book. Smith has advertised for pen pals from her cell. And Rudolph writes essays defending the bombing of abortion clinics, essays that his followers post on the Internet.