When the Supreme Court voided all federal death-penalty laws in June 1972 — despite the Constitution’s clear intent to allow capital punishment — three justices explained that these laws had become "cruel and unusual punishment" because they violated "the evolving standards of decency that mark the progress of a maturing society."

But then, public opinion moved sharply in an unexpected direction. Support for the death penalty soared in the months after the 5-4 decision in Furman v. Georgia. It was 50 percent to 42 percent (an 8-point spread) in March 1972 and 57 percent to 32 percent (a 25-point spread) that November. It kept soaring for two decades, in close sync with crime rates, to a high of 78 percent to 17 percent in the early 1990s. (All numbers are from Gallup polls.)

"Furman, like other landmark cases, had the effect of calling its opponents to action," Stuart Banner wrote in 2002 in The Death Penalty: An American History. One result was the passage of new state death-penalty laws. The justices upheld some of them in 1976 and thereafter because they provided for special hearings to weigh mitigating against aggravating evidence and thus made the process of deciding who dies less capricious (at least in theory). And the number of death sentences pronounced each year by juries rose steadily, to a post-Furman high of 317 in 1996.

But although polls show that about 65 percent of the public still supports capital punishment in the abstract, the number of juries opting for death has plunged, from 317 in 1996 to 128 in 2005, the latest year for which complete data are available. Similarly, the number of executions has dropped from a modern high of 98 in 1999 to 53 in 2006.

At the same time, experts agree, many prosecutors have become more reluctant to seek the death sentence.

As recently as 20 years ago, it was extraordinarily rare for a convicted prisoner to establish his or her innocence conclusively enough to get public attention. That changed with breakthroughs in DNA science.

The 205th DNA exoneration since 1989 was recorded earlier this month by the Innocence Project, a group of crack defense lawyers who have made such cases their mission. The exonerated prisoners — including 15 who had been sentenced to death — have been found innocent by courts, prosecutors, or governors based on post-conviction DNA testing.

But America has been too slow to appreciate that the DNA exonerations, and other evidence, suggest that many thousands of other wrongly convicted people are rotting in prisons and jails around the country. And our federal, state, and local governments and courts have done far too little to adopt proposed criminal justice reforms that could reduce the number of innocent people convicted while nailing more of the real criminals.

The case of the most recent DNA exonoree, Byron Halsey, was typical: Based on a confession full of obviously false details, extracted by high-pressure interrogation, he spent 19 years in prison in New Jersey for two heinous child murders committed by another man in 1985. Halsey was able to prove his innocence only after a 2002 New Jersey law forced reluctant prosecutors to give his counsel access to DNA evidence. In Halsey’s and some 70 other DNA-exoneration cases, DNA also helped to establish the guilt of the real perpetrators. All or almost all had committed other violent crimes before being caught.

Timothy McVeigh is the ideal poster boy for the death penalty, it is often said. He is an unmistakably guilty, unrepentant, rational, calculating, confessed mass murderer who can complain neither of racism (he’s white) nor of an unfair trial (he had good lawyers). If anyone ever deserved execution, he does. Even leading anti-death-penalty scholar Hugo Adam Bedau has said: "I’ll let the criminal justice system execute all the McVeighs they can capture, provided they’d sentence to prison all the people who are not like McVeigh."

Congress and the President have a chance this year to show that they care as much about avoiding the execution (and imprisonment) of innocent defendants as they do about punishing the guilty ones. They can adopt the Innocence Protection Act, a bipartisan proposal co-sponsored by death penalty supporters and opponents who agree that you can be tough on crime without punishing innocent people. The bill would give prisoners expanded access to possibly exculpatory DNA evidence. It would also deliver-if only in capital cases-on the Supreme Court’s long-broken 1963 promise to provide indigent criminal defendants with competent trial lawyers.