An Ohio inmate put to death for murder was tortured by his unusually slow execution, the man's daughter said Friday as she announced plans to file a lawsuit over her father's death.

Dennis McGuire's daughter, Amber, referred to the "agony and terror" of watching her father as he appeared to gasp in his final moments Thursday — using the same words the condemned man's attorneys used in trying to stop his execution using a previously untried method of lethal injection.

"It was the most awful moment in my life to witness my dad's execution," she said in a statement ahead of the news conference. "I can't think of any other way to describe it than torture."

The execution violated Dennis McGuire's constitutional right not to be treated or punished in a cruel or unusual way, said defense attorney Jon Paul Rion, representing McGuire's adult children.

McGuire's attorney Allen Bohnert called the convicted killer's death "a failed, agonizing experiment" and added: "The people of the state of Ohio should be appalled at what was done here today in their names."

It's almost certain lawyers will use McGuire's execution to challenge Ohio's plans to put a condemned Cleveland-area killer to death in March.

McGuire's lawyers had attempted last week to block his execution, arguing that the untried method could lead to a medical phenomenon known as "air hunger" and could cause him to suffer "agony and terror" while struggling to catch his breath.

Nearly 25 minutes before death

A few minutes before McGuire was put to death, Ohio prison director Gary Mohr said he believed the state's planning would produce "a humane, dignified execution" consistent with the law.

McGuire, 53, made loud snorting noises during one of the longest executions since Ohio resumed capital punishment in 1999. Nearly 25 minutes passed between the time the lethal drugs began flowing and McGuire was pronounced dead at 10:53 a.m.

Executions under the old method were typically much shorter and did not cause the kind of sounds McGuire made.

Ohio prisons spokeswoman JoEllen Smith had no comment on how the execution went but said a review will be conducted as usual.

Judges will now realize that the warnings being raised about these untried procedures are not just false alarms. - Richard Dieter, executive director of the Death Penalty Information Center

Prison officials gave intravenous doses of two drugs, the sedative midazolam and the painkiller hydromorphone, to put McGuire to death for the 1989 rape and fatal stabbing of a pregnant newlywed, Joy Stewart.

The method was adopted after supplies of a previously used drug dried up because the manufacturer declared it off limits for capital punishment.

McGuire's attorney called on Republican Gov. John Kasich to impose a moratorium on future executions, as did a state death penalty opponent group.

The move will likely echo across the country as other states contemplate new drug methods, said Richard Dieter, executive director of the Death Penalty Information Center, which opposes capital punishment.

'Not entitled to a pain-free execution'

"Judges will now realize that the warnings being raised about these untried procedures are not just false alarms," he said in an email. "States will now have more of a burden to show that they are using a well thought out best practice. "

What was particularly unusual Thursday was the five minutes or so that McGuire lay motionless on the gurney after the drugs began flowing, followed by a sudden snort and then more than 10 minutes of irregular breathing and gasping. Normally, movement comes at the beginning and is followed by inactivity.

"Oh, my God," Amber said as she watched his final moments.

In pressing for the execution to go ahead, state Assistant Attorney General Thomas Madden had argued that while the U.S. Constitution bans cruel and unusual punishment, "you're not entitled to a pain-free execution."

U.S. District Judge Gregory Frost sided with the state. But at the request of McGuire's lawyers, he ordered officials to photograph and preserve the drug vials, packaging and syringes.

'I'm going to heaven,' convict says

McGuire, strapped to a gurney in the death chamber, thanked Stewart's family members, who witnessed the execution, for their "kind words" in a letter he apparently received from them.

"I'm going to heaven. I'll see you there when you come," he said.

Stewart's slaying went unsolved for 10 months until McGuire, jailed on an unrelated assault and hoping to improve his legal situation, told investigators he had information about the death. His attempts to pin the crime on his brother-in-law quickly unraveled, and he was accused of the killing.

More than a decade later, DNA evidence confirmed McGuire's guilt, and he acknowledged his responsibility in a letter to Kasich last month.

We have forgiven him, but that does not negate the need for him to pay for his actions. - Statement from victim's family

The death row inmate's lawyers argued McGuire was mentally, physically and sexually abused as a child and had impaired brain function that made him prone to act impulsively.

"We have forgiven him, but that does not negate the need for him to pay for his actions," Stewart's family said in a statement after the execution.