LUCASVILLE, Ohio (AP) — A condemned killer appeared to gasp several times and took more than 15 minutes to die yesterday as he was executed with a combination of drugs never before tried in the US.

Dennis McGuire was still for almost five minutes, then emitted a loud snort, as if snoring, and continued to make that sound over the next several minutes. He opened and shut his mouth several times without making a sound as his stomach rose and fell.

“Oh my God,” his daughter, Amber McGuire, said as she observed her father’s final moments. His adult children sobbed in a witness room as they watched him die.

In trying to stop his execution, McGuire’s lawyers had argued that he was at substantial risk of a medical phenomenon known as air hunger, which would cause him to experience terror as he strains to catch his breath.

McGuire, 53, was sentenced to die for the 1989 rape and fatal stabbing of a young pregnant woman, Joy Stewart. He acknowledged that he was responsible in a letter to Governor John Kasich last month.

Ohio’s never-tried lethal injection method was adopted after the maker of the state’s previous drug put it off limits for capital punishment.

Some states that still carry out executions have struggled to find drug supplies for lethal injections after companies refused to supply the drugs for that purpose.

Federal public defender Allen Bohnert called McGuire’s death “a failed, agonising experiment by the state of Ohio”.

Capital punishment continues to be a much-debated subject in the United States. In all, 39 executions were carried out last year, according to the Death Penalty Information Centre.

“I’m going to heaven, I’ll see you there when you come,” McGuire said shortly before his execution. He opened and shut his left hand several times before the drugs took effect, appearing to wave to his children.

Previous executions with the former execution drugs took much less time, and typically did not include the types of snorts and gasps that McGuire uttered.

State attorneys had disputed claims that McGuire would experience terror as he was put to death with the new method.

A lawyer for the state had argued that although the US Constitution bans executions that constitute cruel and unusual punishment, that doesn’t mean procedures are entirely comfortable.

“You’re not entitled to a pain-free execution,” Thomas Madden told a federal judge.

The judge sided with the state but acknowledged the new method was an experiment.

Ohio officials used intravenous doses of two drugs, the sedative midazolam and the painkiller hydromorphone, to put McGuire to death.

“We have forgiven him, but that does not negate the need for him to pay for his actions,” said a statement released by Carol Avery, Stewart’s sister, after McGuire’s death.