In 2008, two years before he announced his retirement, Justice John Paul Stevens reversed course and in a concurrence said that he now believed the death penalty to be unconstitutional

WASHINGTON — In 1976, just six months after he joined the Supreme Court, Justice John Paul Stevens voted to reinstate capital punishment after a four-year moratorium. With the right procedures, he wrote, it was possible to ensure “evenhanded, rational and consistent imposition of death sentences under law.”

In 2008, two years before he announced his retirement, Stevens reversed course and in a concurrence said that he now believed the death penalty to be unconstitutional.

But the reason for that change of heart, after more than three decades on the court and some 1,100 executions, has in many ways remained a mystery, and now Stevens has provided an explanation.

In a detailed, candid and critical essay to be published this week in The New York Review of Books, he wrote that personnel changes on the court, coupled with “regrettable judicial activism,” had created a system of capital punishment that is shot through with racism, skewed toward conviction, infected with politics and tinged with hysteria.

The essay is remarkable in itself. But it is also a sign that at 90, Stevens is intent on speaking his mind on issues that may have been off-limits while he was on the court.

In the process, he is forging a new model of what to expect from Supreme Court justices after they leave the bench, one that includes high-profile interviews and provocative speeches.

Stevens’ death-penalty essay will be published in The New York Review’s Dec. 23 issue and will be available on its website Sunday evening.

The essay is actually a review of the book “Peculiar Institution: America’s Death Penalty in an Age of Abolition,” by David Garland, a professor of law and sociology at New York University.

The book compares American and European approaches to the death penalty, and Stevens appears to accept its major conclusions.

Garland attributes American enthusiasm for capital punishment to politics and a cultural fascination with violence and death.