Arizona execution takes two hours
US death row inmate Joseph Wood has died after an execution in Arizona took nearly two hours to kill him.
Wood, a double murderer, was executed by lethal injection.
His lawyers filed an appeal for an emergency stay of execution, after he had been "gasping and snorting for more than an hour" in the death chamber.
Arizona Governor Jan Brewer says she has ordered a full review of the execution, although she said that Wood "died in a lawful manner".
Wood's lawyers argued the extended execution process violated his right to be executed in the absence of cruel and unusual punishment.
But Ms Brewer said: "By eyewitness and medical accounts he did not suffer. This is in stark comparison to the gruesome, vicious suffering that he inflicted on his two victims, and the lifetime of suffering he has caused their family."
Drug source questions
The execution should have taken 10 minutes, his lawyers said, but Wood, 55, gasped more than 600 times before he died.
It began at 13:52 (20:52 GMT), and Wood was pronounced dead at 15:49, one hour and 57 minutes later, according to the Arizona attorney-general's office.
He was convicted of the 1989 murders of his estranged girlfriend Debra Dietz and her father Eugene Dietz.
Family members of the victims were unconcerned by the way the execution was carried out.
"This man conducted a horrific murder and you guys are going, let's worry about the drugs,'' said Richard Brown.
"Why didn't they give him a bullet?"
Wood's lawyers had sought to force Arizona to name the manufacturers of the drugs used in the execution, but a last-ditch ruling by the US Supreme Court cleared the way for the execution to go ahead.
Analysis: Rajini Vaidyanathan, BBC News, Washington
This latest case has brought the issue of how America executes its inmates on death row back into the spotlight, only a few months after a botched execution in Oklahoma.
The US constitution prohibits punishment which is "cruel and unusual". These cases, and the secrecy around the source of lethal injection drugs, will be cited by opponents as another reason to abolish capital punishment.
With more states failing to get hold of the chemicals, some are looking for alternatives. Earlier this month Tennessee introduced a law to bring back the electric chair, if there are no supplies of the drug. But this too is likely to be subject to legal challenges.
There might be an outcry over this latest execution, but the death penalty is still supported by many in the US, especially in southern states where most executions take place. Many argue it is a just punishment for those who have committed the most heinous of crimes.
In communications with Wood's lawyers this year, Arizona officials said they would use a two-drug combination of midazolam and hydromorphone to put him to death.
But they declined to provide further identifying information, including the name of the drug's manufacturer, citing a state confidentiality law aimed at protecting the drug makers from reprisal.
In 2010, the sole US manufacturer of sodium thiopental, a sedative used in lethal injections, stopped producing it. States switched to pentobarbital, also a sedative, but its Danish manufacturer Lundbeck began tightly restricting its distribution to prevent it being used in executions.
And in 2011, the UK imposed export bans on three common lethal injection drugs, pentobarbital, pancuronium bromide and potassium chloride. In the same year, the EU restricted the distribution of sodium thiopental to nations that practise capital punishment.
States have experimented with other drugs since.
In April, Oklahoma tried to inject Clayton Lockett with a dose of midazolam, but the executioners were unable to find a suitable vein, the injection failed, and the execution was halted. Lockett died of a heart attack moments later.
And in January in Ohio, Dennis McGuire appeared to gasp, snort and choke for 25 minutes after he was injected with a two-drug combination of midazolam and hydromorphone.