My recollections of the one execution I attended amount to memories of a ghastly, surrealistic encounter with justice. The condemned prisoner lay covered with a sheet, which hid from the witnesses the intravenous lines threaded into both of his arms.

Sitting just a few yards away, I held the hand of his wife, who wept, prayed and spoke in tongues as the ritualistic killing unfolded. The inmate said goodbye to her, to his lawyers, to his spiritual advisors. Then the series of poisons entered his bloodstream, and he breathed in a labored manner, gradually turning a deep purple, and died.

In all respects it was a calm, orderly, cold-blooded and super-premeditated killing of one human being by another. Stripped of the sanction of law, the execution could have served as a perfect example of first-degree murder, punishable by death in 32 states in America.

Needless to say, the execution of that man, in 1995, was vastly different from Oklahoma's ghoulishly botched attempt to execute Clayton Lockett on Tuesday night.

As the world is now well aware, my state's effort to execute two prisoners in the same day for the first time since 1937 turned into a horrible miscarriage. We should have seen it coming, of course, as the secrecy and the scarcity of the drug cocktail in the execution mixed with the bickering and the borderline constitutional crisis in the halls of Oklahoma government, where all hell was breaking loose. Until, that is, hell came to the death chamber.

Lockett's body twitched before he attempted to sit up, began to nod, mumbled and writhed, was injected with a failed sedative, revived, then suffered a "vein failure", and died, of a massive heart attack, nearly 45 minutes later.

Botched lethal injections are hardly rare, and the protocols and drugs used vary from state to state – from a gasping inmate in Ohio, to the Oklahoma man whose last words were "my whole body is burning", to Texas and Florida and beyond.

In 1972, the US supreme court declared a moratorium on executions after determining that the death penalty was being imposed in an arbitrary and capricious manner. The lack of standards in capital cases caused the high court to equate being sentenced to death to being struck by lightning.

When the supreme court reinstated the death penalty four years later, it didn't establish a one-size-fits-all process for capital cases. Instead, as is true of criminal justice in general, the court recognized that states were free to craft their own death penalty procedures, and each state could serve as a laboratory.

By submitting different processes to the crucible of adversary testing at the state level, the legal thinking went, surely the best and most reliable decisions about who deserved to die would be made – of course the most humane method of execution would emerge. The past 38 years have demonstrated that this undeniably laudable goal, to let America's laboratories of democracy kill as they see fit, has been far from realized.

The constitutional prohibition on cruel and unusual punishment, as understood by the 2008 US supreme court decision in Baze v Rees, is designed to prevent the gratuitous infliction of unnecessary pain and suffering on those each state seeks to kill. The notion, again, appears to be that states which choose to kill killers should endeavor to occupy a higher moral plane than those whose crimes have merited their extermination.

However, as execution drugs become increasingly scarce, death states are forced to experiment with substitute drugs, to tinker with dosages, to rely on questionable suppliers. Shielding these drugs and their sources from public scrutiny greatly enhances the risk of an unnecessarily painful and consequently unconstitutional execution.

In a tragic sense, Clayton Lockett's agonizing death was the result of a failed experiment. He was convicted of shooting of 19-year-old Stephanie Neiman and reportedly watched as accomplices buried her alive, but justice requires better than bad chemistry. Given that lethal injection is the execution method in all 32 death states, as well as the military and federal government, we can expect that other human science experiments will result in unconstitutional executions.

Now is the time to ask: what progress has really been made since the supreme court's short-lived moratorium on executions? Today, blacks, who comprise roughly 13% of the American population, account for 42% of the death row population. Since 1973, around 140 prisoners have been released from death row with evidence of their innocence. The death penalty remains a punishment most likely to be imposed in cases involving poor minority defendants accused of killing white victims.

Governors in two death penalty states – Washington and Oregon – have imposed moratoriums on executions. Five other states (Kansas, New Hampshire, Pennsylvania, Connecticut and New Mexico) have either performed no executions or have only executed volunteers.

The former supreme court Justice Harry Blackmun was right about what he said way back in 1994: the time "to concede that the death penalty experiment has failed" and to "stop tinker[ing] with the machinery of death" is long overdue.

Now is the time for the supreme court to step in, once again, and impose a nationwide moratorium on executions. These justices may never end capital punishment themselves, but America has more than enough reasons for pause. When the majority of death sentences are reversed, the efficacy of the entire capital punishment system gets called into question. A majority of justices agree that the death penalty does not deter would-be killers. In economic terms, death penalty cases are far more expensive than cases which result in life without parole sentences.

The exercise by a state of its most awesome power – the power to deprive a citizen of his life – must be accompanied by due process and complete transparency. A government which seeks to kill its citizens by way of a process veiled in secret – that is a government which does not deliver justice.