Convicted killer Troy Clark has joked and giggled his way through his execution inside America's most notorious death chamber.

Clark dared a jury to sentence him to death at his trial in 2000 — and got his wish — but spent the next 18 years protesting his innocence.

The 51-year-old was condemned for torturing, beating and drowning his former flatmate Christina Muse in the bathtub of their East Texas home in May 1998.

He was suspected of two other murders but only convicted for the death of Ms Muse.

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Authorities said Clark, a former drug dealer, killed out of fear Ms Muse was going to report his activities to police.

Witnesses to Wednesday's execution have described the killer's surreal final moments before authorities administered a lethal cocktail of drugs by remote control inside America's most notorious death chamber, Huntsville, where more than 500 prisoners have died since 1982.

Clark chuckled as he addressed several friends watching through a window a few feet from him, telling them repeatedly that he loved them and "it's all good".

"I'm not the one who killed Christina," he said. "But, hey, whatever makes you happy."

As the lethal dose of the sedative pentobarbital was administered, Clark was laughing and remarked that the drug "burned going in", according to AP.

Death row inmate Troy Clark protested his innocence until the bitter end. Photo / Texas Department of Criminal Justice
Death row inmate Troy Clark protested his innocence until the bitter end. Photo / Texas Department of Criminal Justice

"I feel it," he said. Then he grunted, gasped and began to snore. Seconds later, all movement stopped. He was pronounced dead 21 minutes later at 6.36pm (around 10.30am Australian time).

Just before his execution, anti-death penalty advocates released a log of Clark's final three days.

The log was mind-numbingly uneventful, including details such as: "sitting on bunk listening to headphones" and "sleeping".

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THE KILLING

Before her brutal murder, Christina Muse, 20, had briefly lived with Clark as a roommate in Tyler, Texas, a city famous for its rose cultivation.

Prosecutors say when she moved out, Clark became paranoid she would tell police he had been dealing methamphetamine.

One day in May 1998, Ms Muse came around for a visit and Clark decided to silence her forever. He subdued her with a stun gun, bound her with duct tape and locked her in a wardrobe for several hours while he played video games and sold drugs to a customer.

Clark later moved Ms Muse to a bathroom where he smashed her over the head with a board and intimidated his girlfriend and co-defendant, Tory Gene Bush, into helping him drown the victim in the bathtub.

Death row inmate Troy Clark protested his innocence until the bitter end. Photo / Texas Department of Criminal Justice
Death row inmate Troy Clark protested his innocence until the bitter end. Photo / Texas Department of Criminal Justice

Ms Muse's body was then stuffed into a 55-gallon barrel with cement mix and lime before being dumped in a ravine.

Four months later, Bush helped lead police to Ms Muse's body in the ravine off Texas Highway 64, west of Tyler, on a property owned by Clark's landlady.

Police also found the body of Tracy Mize floating in a septic tank on the property.

Ms Mize had been a defendant in a federal drug case and promised information on the murder in exchange for leniency.

Investigators believe Clark shot Ms Mize after learning she had turned informant.

"When you actually are out in a field, and you see a barrel with a woman's body being taken away and a septic tank is opened up and you see another individual floating face down in it, it really grips you," prosecutor David Dobbs later told media.

'I JUST WANT THE DEATH PENALTY'

During his trial for the murder of Christina Muse, the state presented witnesses who claimed Clark had killed two others, Tracey Mize and another man, as well as raped a woman.

He was not charged with any of the other crimes and pleaded not guilty to Ms Muse's murder.

Against his lawyers' advice, Clark took the stand at his sentencing hearing, telling the jury, "I really ain't got no story to tell. It's just I want the death penalty."

He did not allow anyone else, including his parents, to testify on his behalf.

Clark's co-defendant Tory Bush testified against him at his trial, describing Ms Muse's horrific final moments in detail.

Death row inmate Troy Clark's final three days were logged in mind-numbing detail. Photo / Twitter
Death row inmate Troy Clark's final three days were logged in mind-numbing detail. Photo / Twitter

She said Clark attacked the young woman with the stun gun saying: "You should have kept your mouth shut.'

Bush told jurors she helped Clark remove Ms Muse from the wardrobe — where she'd been locked for several hours — and carry her to the bathtub.

She said Clark then ordered her to fetch him a heavy wooden board which he used to bludgeon his victim. Bush claimed she left the bathroom but could hear Ms Muse being hit with the board.

Bush said when he called her back into the bathroom, she saw blood all over the wall behind the tub, which Clark had begun filling with water.

He then threatened Bush to help him drown Ms Muse by holding her head underwater.

Bush testified she went out to buy lime at Clark's request and that Clark had already begun disposing of Ms Muse's body by the time she returned.

The next day, Clark, Bush and three friends helped dispose of the barrel containing the victim's body in a ditch. The friends, who allegedly had no idea what they were helping with, also testified against Clark.

"I have no doubt in my mind that Troy Clark killed Christina Muse and Tracy Mize," prosecutor David Dobbs told the jury.

"I'm not an expert on what causes this. I'm not an expert on what mitigation may have happened in his life. I just know that my job as a prosecutor for Smith County was to make sure our streets are safe. And our streets are safe without Troy Clark on them."

On March 30, 2000, Clark was sentenced to death. The Texas State Court of Criminal Appeals upheld the judgment and sentence on mandatory appeal.

Death row inmate Troy Clark in his mugshot after his 1999 arrest. Photo / Texas Department of Criminal Justice
Death row inmate Troy Clark in his mugshot after his 1999 arrest. Photo / Texas Department of Criminal Justice

Tory Bush pleaded guilty to her role in Ms Muse's murder and was jailed for 20 years.

After his conviction, Clark had argued his trial attorneys failed to present evidence of his childhood, marked by physical and emotional abuse as well as foetal alcohol syndrome, which might have convinced jurors to spare his life.

Appeals courts had previously ruled that because of the overwhelming case against him, it was unlikely jurors would have shown him any leniency even if they'd known about his troubled history.

Clark is the 17th inmate put to death this year in the US and the ninth given a lethal injection in Texas, the nation's busiest capital punishment state.

He is the first of two inmates scheduled to die this week, with Daniel Acker set to die tomorrow for fatally running over his girlfriend.

At least eight other Texas inmates have planned execution dates in the coming months.