A list of executions that went wrong in U.S. from 2006 to 2014:
Joseph L. Clark
Convicted of murdering a man during a gas station holdup
Execution: May 2, 2006, in Ohio
After technicians spent 22 minutes searching for a suitable vein, Mr. Clark's arm began to swell. He then raised his head off the gurney and said five times: "It don't work." Technicians then spent another 30 minutes before finding a suitable vein. Journalists later reported hearing "moaning, crying out and guttural noises." Death was pronounced 90 minutes after the process began.
Angel Nieves Diaz
Convicted of murdering a strip-club owner
Execution: Dec. 13, 2006, in Florida
After the first injection was administered, Mr. Diaz squinted and grimaced as he tried to mouth words A second dose was then administered and about 34 minutes later, Mr. Diaz was declared dead.
Convicted of murdering a cellmate after an argument over a chess game
Execution: May 24, 2007, in Ohio
Medical staff struggled to find a vein in Mr. Newton's arms, jabbing him at least 10 times. He was declared dead almost two hours after the execution process began.
Convicted of murdering his wife and her two daughters
Execution: June 26, 2007, in Georgia
Medical staff spent about 40 minutes finding a suitable vein to administer lethal chemicals. Death was not pronounced until 59 minutes after the execution process began.
Convicted of murdering a man and a woman to avoid paying a $400 debt
Execution: June 4, 2008, in Georgia
After a 55-minute delay while the U.S. Supreme Court reviewed a final appeal, prison medical staff struggled for 35 minutes to find a suitable vein. Then it took 14 minutes after lethal drugs were administered before death was pronounced.
Convicted of raping and murdering a 14-year-old girl
Execution attempt: Sept. 15, 2009, in Ohio
Mr. Broom's execution was terminated after medical staff were unable to find a useable vein in his arms or legs, blaming the problem on his history of intravenous drug use. Ohio Governor Ted Strickland then announced physicians would be consulted on a more efficient method. Five years later, he remains on death row awaiting an Ohio Supreme Court appeal ruling on whether a do-over would be cruel and unusual punishment or violate double-jeopardy rules.
Brandon Joseph Rhode
Convicted of killing a man and his son and daughter during a burglary
Execution: Sept. 27, 2010, in Georgia
After the Supreme Court rejected his appeals, medics tried for about 30 minutes to find a vein to inject a lethal concoction. It then took 14 minutes until death was pronounced. The execution had been delayed six days because a prison guard had given Mr. Rhode a razor blade which he used to attempt suicide.
Convicted of raping and stabbing to death a pregnant newlywed
Execution: Jan. 16, 2014, in Ohio
Mr. McGuire gasped for air for 26 minutes before dying. Witnesses said after the injection, Mr. McGuire struggled, with his stomach heaving and fists clenched, making "horrible" snorting and choking sounds.
Clayton D. Lockett
Convicted of shooting a woman with a sawed-off shotgun and watching as two accomplices buried her alive
Execution: April 29, 2014, in Oklahoma
Mr. Lockett writhed in pain as a needle became dislodged during his injection. The process was then halted, but he died shortly after of a heart attack 43 minutes after the execution began.
Source: U.S. Death Penalty Information Center