In his latest book, Six Amendments: How and Why We Should Change the Constitution, retired United States Supreme Court Justice John Stevens reminds us why some of the most frustrating judges are the ones who have left their courts behind. What would American law look like today, how different might it be, if this moderate justice had been willing to vote on the Court all those decades for what he now believes to be just?

For example, a man who consistently upheld capital convictions and the death penalty itself for over 35 years, who helped send hundreds of men and women to their deaths by failing to hold state officials accountable for constitutional violations during capital trials, who more recently endorsed dubious lethal injection standards because he did not want to buck up against court precedent, now wants the Eighth Amendment to read this way, with five new words added:

Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments such as the death penalty inflicted.

It's never too late for redemption, I suppose (unless you are one of those innocent men executed in America since capital punishment returned in its modern form in 1976). And Justice Stevens deserves credit, at least, for sharing his change of heart with the rest of the world in a manner likely to garner much attention. In his new book, a wish-list of what he'd like to change about the Constitution, an apology of sorts for all that he got wrong, he writes:

For me, the question that cannot be avoided is whether the execution of only an "insignificant minimum" of innocent citizens is tolerable in a civilized society. Given the availability of life imprisonment without the ability of parole as an alternative method of preventing the defendant from committing further crimes and deterring others from doing so, and the rules that prevent imposing an "eye for an eye" form of retributive punishment, I find the answer to that question pellucidly clear. When it comes to state-mandated killings of innocent civilians, there can be no "insignificant minimum."

These are powerful words—and perhaps they will further stoke the roiling debate today over the death penalty. But they are essentially the same words uttered famously, for essentially the same reasons, by another moderate Republican appointee, Justice Harry Blackmun. It's been 20 years now since he turned away from the death penalty in Callins v. Collins in one of the most famous dissents in Court history. In February 1994, Justice Blackmun wrote:

Rather than continue to coddle the Court's delusion that the desired level of fairness has been achieved and the need for regulation eviscerated, I feel morally and intellectually obligated simply to concede that the death penalty experiment has failed. It is virtually self evident to me now that no combination of procedural rules or substantive regulations ever can save the death penalty from its inherent constitutional deficiencies. The basic question—does the system accurately and consistently determine which defendants "deserve" to die?—cannot be answered in the affirmative.

Twenty years later, with what we now know about wrongful convictions, racial disparities in capital cases, and lethal injection secrecy, those words ring ever more true. Now compare Justice Blackmun's cri de coeur with the words of Justice Stevens, in the aforementioned lethal injection case, Baze v. Rees, decided in 2008. In a concurrence in that case, after a lengthy critique of capital punishment rules and Kentucky's lethal injection plans, Justice Stevens wrote:

I have relied on my own experience in reaching the conclusion that the imposition of the death penalty represents “the pointless and needless extinction of life with only marginal contributions to any discernible social or public purposes. A penalty with such negligible returns to the State [is] patently excessive and cruel and unusual punishment violative of the Eighth Amendment.” Furman, 408 U. S., at 312 (White, J., concurring).

It took Justice Stevens over 30 years—from his ascension to the Supreme Court in 1975 to 2008—to reach this point. And it has taken him another six years, from 2008 to 2014, to fully become the advocate for reform that he never was on the Court. If I were Senator Patrick Leahy, the Vermont Democrat who chairs the Senate Judiciary Committee, I would invite Justice Stevens today to testify on Capitol Hill about the death penalty—to bear witness, expert witness, to its arbitrary nature.