ST. LOUIS

- A bungled execution in Oklahoma provides death-penalty opponents with a fresh, startling example of how lethal injections can go wrong. But the odds of successfully challenging the nation's main execution method will probably hinge on exactly what caused the apparent agony of inmate Clayton Lockett.

The state was using a new lethal-drug combination for the first time in Tuesday's execution in McAlester, Okla. If Lockett suffered because of a collapsed vein or improperly inserted IV, the legal landscape might not change much. If the drugs or the secrecy surrounding them played a role, defense lawyers for other prisoners could have powerful new evidence to press the Supreme Court to get involved, legal experts say.

A day after the execution went awry, some lawyers for death-row inmates began planning new appeals or updating existing cases based on events in Oklahoma. Many called for moratoriums and independent investigations.

"Every prison is saying, 'We have it under control, trust us,' " said Texas lawyer Maurie Levin, who spent yesterday preparing new briefs questioning that state's execution practices. "This just underscores in bold that we can't trust them, and prisons have to be accountable to the public and transparent in the method by which they carry out executions."

Lockett, 38, convicted of shooting a woman and watching as two accomplices buried her alive, was declared unconscious 10 minutes after the first of three drugs was administered. Three minutes later, he began to breathe heavily, writhing, clenching his teeth and straining to lift his head off the pillow. Authorities halted the execution, but Lockett died of a heart attack more than 40 minutes after the process began.

Meanwhile, Oklahoma Gov. Mary Fallin named a member of her Cabinet yesterday to lead a review of how the state conducts executions after a botched procedure that the White House said fell short of the humane standards required.