The study, which looked at all death-penalty cases across the country from 1973 to 1995, showed that 68 per cent of capital convictions were overturned because of incompetent defence counsel, misconduct by police or prosecutors, or judges misdirecting juries.

Reported errors ran the gamut from defence lawyers falling asleep in court, to prosecutors keeping African Americans off the jury when a black defendant was being tried, to judges badmouthing defendants to the media in the middle of trials.

The findings deal a serious blow to the only remaining system of capital punishment in the Western world. In recent months, new DNA evidence has challenged many death penalty convictions, leading to an almost unprecedented erosion in public support and causing politicians in two conservative states, Illinois and New Hampshire, to take steps to stop executions altogether.

James Liebman, a Columbia University law professor, former criminal defence lawyer and lead author of the study, said the figures revealed a system that was "wasteful and broken" and raised questions as to whether other judicial errors had gone unnoticed.

Of the cases where death sentences were challenged on appeal, 75 per cent led to lesser punishments and 7 per cent led to a final verdict of not guilty. Even in the 18 per cent of cases where the death penalty was reapplied on retrial, further appeals often led to sentences being overturned again.

Three states, Kentucky, Maryland and Tennessee, had been unable to make a single death sentence stick since the reintroduction of capital punishment in the early 1970s. Nine other states, including California and Georgia, had reversal rates of more than 80 per cent. And although two of the states that carry out the most executions, Texas and Virginia, were near the bottom of the list (52 per cent and 18 per cent respectively), Professor Liebman said this could be a commentary on their inability to spot errors rather than an indication of greater judicial competence.

The litany of errors, and the excruciatingly long time it takes to uncover them – nine years in a typical judicial review, and more than twice that long in some cases – was exacting "terrible costs on taxpayers, victims' families, the judicial system and the wrongly condemned", Professor Liebman concluded.

Of the 5,760 death sentences passed during the study period, only 313 – less than 5 per cent – were actually carried out, raising questions about both the efficiency of the system and the psychological cruelty imposed on death-row prisoners.

"It's not just one case, it's not just one state. Error was found at epidemic levels across the country," Professor Liebman said. "From the point of view of a taxpayer, I am paying all this money and they're managing to carry out just one in 20 death sentences."

The study, originally commissioned by the Senate Judiciary Committee as a scientific analysis of judicial error, took nine years to complete but arrived at the most sensitive time possible, when the issue has entered the presidential election campaign because of the unprecedented rate of execution championed by the Republican candidate, the Texas Governor, George W Bush.

Texas has almost doubled the number of its executions since 1995, the end of the study period and the year Mr Bush first became governor. Human rights groups have increased their accusations of violations of due process in that time – claiming the Texas system knowingly provides inadequate counsel to defendants unable to pay for their own lawyers to hurry the system along and save money.

Supporters of the death penalty, including the staff of Governor Bush, tried to minimise the impact of the Liebman study, arguing that the high rate of reversals was an indication that the system was working, the result of the thoroughness of the courts rather than their sloppiness.

One Bush spokesman, Ari Fleischer, chose to focus not on the 68 per cent figure but rather on the 7 per cent of death-row prisoners eventually exonerated of the crimes laid at their door. "This shows that 93 per cent are still found guilty," Mr Fleischer said. "It's not an error about their innocence. It's just a question of the appropriate punishment."

But a chorus of commentators took the opposing viewpoint. "There should be zero tolerance for mistakes, not a 60 to 70 per cent tolerance for mistakes," said Patrick Leahy, a Democratic Senator for Vermont and a long-standing opponent of the death penalty. "You certainly could not run a public utility or an airline or a hospital that way."

Senator Leahy was one of a group who put together draft legislation last week that would give death-row prisoners the automatic right to present DNA evidence not available at their original trial. The Senate will conduct hearings on the issue later this week.

Several former death-penalty advocates, including the televangelist Pat Robertson and the conservative newspaper columnist George Will, have expressed doubts about judicial executions in recent months, particularly since the introduction of DNA evidence that has thrown the previous certainty of the criminal courts into deep confusion in several states.

Stephen Saltzburg, a former Justice Department official in the Reagan administration, which supported capital punishment, said of the new study: "It must make any fair-minded person wonder what is wrong with the death-penalty system around the country."

The death penalty remains overwhelmingly popular in the US, with about two-thirds of the population supporting it, but opinion polls show it has recently hit a 22-year low in public favour. The development of DNA testing has been responsible for rocking confidence in a number of convictions, some of them stretching back two decades or more, and was instrumental in persuading Illinois' conservative Governor, George Ryan, to call a halt to executions in his state because of 13 cases in which the guilt of the defendant was thrown into serious doubt.

In one case, the defendant, Anthony Porter, went through the court system without any error being detected. Less than 48 hours before he was due to die, he was granted a stay because a psychologist's test showed he had an IQ of less than 50 and might not be mentally competent. Journalism students at Northwestern University subsequently uncovered evidence that exonerated him altogether.

Copyright 2000 Independent UK

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