The small room is silent and the desk fan that whirs by the door fails to cut through the muggy warmth. There are 24 black metal chairs, in two rows of 12, and two boxes of tissues, one placed somewhere near the middle of each row. I'm told to sit at the back, at the far end, and the female corrections officer standing a few feet away doesn't acknowledge me as I take my seat; instead she stands there, silently staring at her fingernails. There's another guard at the other end of the room - by the yellow door I just came through - and two men in suits, each of whom has a black phone pressed to his ear.

Seven people - six men and one woman - are then escorted through that yellow door and take their seats in front of me. One of them, an older man in his seventies, removes a large cowboy hat then says something quietly to the guard. She smiles but doesn't reply.

Nobody else says a word; etiquette perhaps dictates that you don't speak once inside this room.

A few seconds later the curtain we are facing opens. Behind the glass a woman wearing a smart jacket and skirt faces us from where she stands, behind a hospital gurney in the centre of the room.

Arkansas executed Ledell Lee, the first of eight condemned prisoners that state had hoped to kill in the space of 11 days on Thursday night, 20 April. Lee was pronounced dead at 11.46pm local time. © Rex / Shutterstock

Lying on the gurney is a man in his fifties with grey hair and glasses. His head rests on a pillow and his large body is covered by a crisp white sheet. He has two IV needles taped to his arms and I notice a little dried blood above the plasters. He tilts his head slightly to acknowledge the people sitting in front of me. He begins to cry. This is Kenneth Hogan and in a little more than ten minutes he'll be dead.

Two weeks earlier, on 9 January, another man was lying on this same gurney, covered in a crisp white sheet. Michael Lee Wilson was 38 and had been on death row for his part in the killing of a colleague who worked in an Oklahoma convenience store. As the drugs took hold Wilson said into the microphone above him, "I feel my whole body burning."

This is Kenneth Hogan and in a little more than ten minutes he'll be dead.

Perhaps Wilson knew, or perhaps he didn't, that those words would outlive him; that they'd form part of a litany of horrifying testimony that would put the lethal-injection process in the United States on trial.

Until the Eighties, when a syringe was routinely used to pump death-row inmates full of lethal drugs, the electric chair was the de facto method of killing criminals in the US. The chair is still retained in eight states in the event that an inmate chooses it over lethal injection (which one did as recently as last year), the lethal injection drug supply dries up, or the method is ruled unconstitutional. With the electric chair, electrodes are fastened to the condemned prisoner's head and legs and around 2,000 volts are sent through their body.

There have been problems with the chair ever since it was first employed in 1890 in New York. Then, a vegetable seller called William Kemmler, who had killed his girlfriend with a hatchet, was strapped in, and after convulsing as the electrical current surged through his body a doctor pronounced him dead.

His diagnosis, however, was premature. "Great God," cried one witness, "he's alive." "Turn on the current," shouted another.

Unconscious but still breathing, Kemmler was then subjected to another bolt of electricity. According to a New York Times report at the time, "blood began to appear on the face of the wretch in the chair", and afterwards the deputy coroner told the correspondent, "I would rather see ten hangings than one such execution as this."

In 1999, photographs of the botched electrocution of Allen Lee Davis on Florida's death row were published by a judge on the state's supreme court. In the pictures, Davis can be seen purple-faced, eyes scrunched shut, blood pouring from his nose and dripping onto his prison whites. The sickening spectacle drew nationwide media attention and an end to Florida's use of the electric chair.

But electrocution was used in another state as recently as January 2013, when Robert Gleason Jr, 42, who strangled his cell mate in prison, was executed by the state of Virginia. In fact, in the past decade, seven inmates - all men - have been executed this way, in South Carolina, Virginia and Tennessee.

Two new drugs being used for lethal injection in Ohio

The gas chamber was introduced in 1924 in an effort to improve on electrocution but that hasn't fared much better. In 1983, murderer Jimmy Lee Gray was executed by the state of Mississippi and a report described how, as Gray began inhaling the toxic fumes, he thrashed his head around, repeatedly banging it into an iron bar behind his chair until he lost consciousness. In 1996, a panel of judges in California (where the gas chamber had been used since 1933) ruled that it constituted a "cruel and unusual punishment".

But each state makes its own laws, and the gas chamber is still authorised in three states - Arizona, Missouri and Wyoming.

Hanging is still available in Delaware, New Hampshire and Washington state, and firing squad in Oklahoma (if lethal injection or electrocution are ever found unconstitutional). Utah abolished the firing squad in 2004 for any new death-row inmates, but that's how four men currently on death row there will be executed because they were "grandfathered in" when they elected it.

According to a local report, when the injection began Brooks closed his eyes, after which he started gasping and wheezing.

In 1977, Jay Chapman, then the Oklahoma state medical examiner, designed a three-drug cocktail that could be used to execute offenders. It consisted of sodium thiopental, an anaesthetic which would put the inmate to sleep; pancuronium bromide, a muscle relaxant; and potassium chloride, which stops the heart. They were to be administered in sequence. Eventually all states that carried out executions (currently 35) would employ lethal injection as their primary method of killing prisoners.

Not surprisingly, considering its less-than-salubrious distinction of being the state that carries out the most executions, Texas was the first to use the three-drug procedure, in 1982, when it put to death 40-year-old Charles Brooks Jr for murdering a car mechanic.

According to a local report, when the injection began Brooks closed his eyes, after which he started gasping and wheezing. He was pronounced dead seven minutes later.

Anaesthetists noted that the second drug, pancuronium bromide, seemed to serve no purpose other than to stop the inmate's body from moving, making watching him die more palatable to witnesses.

As one anaesthetist told me, "It was included to make it prettier."

In 2003, I researched this very same issue after a lawsuit was filed on behalf of Texas death row inmates pointing out that the use of pancuronium bromide was forbidden in Texas - and at least 18 other states - for use by vets in putting animals to sleep. Back then, Jim Marcus, executive director of the Texas Defender Service which filed the suit, told me there was evidence the drug "renders a person paralysed but they're completely sentient and dying a slow death of asphyxiation".

Around the same time, a judge in Tennessee wrote that its use "taps into every citizen's fear that the government manipulates the setting and gilds the lily."

The use of the three-drug cocktail, though, would continue.

Megan McCracken, an attorney at the Death Penalty Clinic at UC Berkeley School of Law, told me that if the first drug isn't administered properly there's a risk of the inmate being awake and aware but paralysed. If that's the case, she said, the third drug, potassium chloride, would cause "extraordinary pain as it travels through the circulatory system".

Execution by lethal injection has been far from devoid of problems. In 1992 in Oklahoma's death chamber, Robyn Parks had a violent reaction to the drugs when the muscles in his jaw, neck and abdomen went into a spasm and he gasped and gagged until he died.

In 2005, in Delaware, the main IV line became blocked during the execution of Brian Steckel. The sedative drug wasn't administered properly, and Steckel stayed conscious as the pancuronium bromide trickled into his vein. According to Fordham University law professor Deborah Denno, Steckel then started to convulse.

In 2007, due to his weight, it took around an hour and a half to find a vein in Christopher Newton's arms as he lay on the gurney in Ohio waiting to die - so long, in fact, that Newton was granted a toilet break. When he was finally injected with the lethal drugs, his stomach heaved, his mouth twitched and he suffered convulsions.

It took 16 minutes to kill him.

Until 2009, the drugs used in the lethal injection process were all available on the US market from wholesalers, but that year Hospira, the sole producer of sodium thiopental, had a manufacturing problem at its plant in North Carolina. Suddenly, according to McCracken, the stocks of sodium thiopental became scarce. "And slowly, you saw departments of corrections running out and unable to get more."

Sodium thiopental had been used less and less in conventional medicine, replaced largely by propofol, a more effective anaesthetic because patient recovery is quicker. McCracken says departments of corrections then began trading with each other and looking to import sodium thiopental from overseas.

Following an investigation by British-based human rights charity Reprieve, it transpired that one of these overseas suppliers was a UK company called Dream Pharma Ltd, run by a man called Mehdi Alavi who rented a desk in a driving school in Acton, London. What's more, he was supplying drugs to the Arizona Department of Corrections that had already been used in at least one execution.

Clive Stafford Smith, Reprieve's ballsy director and an attorney who had spent years working capital murder cases in Louisiana, didn't mince words in a letter to Alavi. "You have played a significant role and hold responsibility for the potential deaths of many people in the United States," he wrote. "I need hardly point out that your advertising slogan - 'Dream Pharma Ltd, Dedicated to the Healthcare of the Public' - is hardly appropriate, unless your dreams refer to Hamlet: 'To sleep, perchance to dream... for in that sleep of death who knows what dreams may come.'"

According to Maya Foa, strategic director of Reprieve's death-penalty team, death-penalty drugs were now being obtained through a complex supply chain and network of global distribution.

This marked the start of a deliberate and very effective campaign on the part of human-rights groups and defence attorneys to thwart the supply of those overseas drugs, through both media campaigns and lawsuits.

Kayem Pharmaceutical Private Limited based in Mumbai, India, supplied sodium thiopental to South Dakota and Nebraska. When it became public knowledge in the spring of 2011, the company's managing director, Naveen Verma, claimed he had no idea what the drugs were being used for, adding that a broker negotiated the contract and had since been sacked.

Somewhat ironically, India retains capital punishment for certain serious offences, though it has only been carried out four times in the past 20 years.

McCracken says this was when some US states began changing the drug protocol they used to carry out lethal injections. When stocks of sodium thiopental dried up, Ohio, for example, changed to a single dose of pentobarbital.

Pentobarbital works much like sodium -thiopental. In our brain we have what are called GABA receptors - chemical messengers that scientists believe control our fear or anxiety when our neurons are overexcited. Pentobarbital and sodium thiopental stimulate those receptors and a certain amount can put you to sleep.

According to one anaesthetist who has researched the lethal injection process, pentobarbital kills people in two different ways: an older, sicker person's veins will dilate and their heart will beat faster, which can cause a heart attack. Younger people whose heart can tolerate the drug stop breathing. And if you stop breathing for five minutes you get brain damage and then hypoxemia - a lack of oxygen in the bloodstream, which will ultimately kill you.

Lundbeck, a Danish pharmaceutical company, held the only licence to manufacture pentobarbital, known by its trade name Nembutal in the United States, and by July 2011, caving to pressure from human-rights groups, it agreed to halt distribution of the product to prisons in any state that carried out the lethal injection. "It appeared to work well," says McCracken. Departments of corrections were unable to get their hands on sedatives used in the lethal injection process and the stocks that some of them did have expired in November of the same year.

Governor of Oklahoma, Mary Fallin © PA Photos

To illustrate just how shady the entire thing had become, one death-penalty attorney shared a redacted email chain with me which showed a foreign supplier of pentobarbital willing to ship to the US using "diplomatic seals", which it said "will enable the parcel to pass free from all customs control and police intervention". The same email claimed it wrapped merchandise in carbon photo paper so that x-ray machines would not penetrate it.

In the spring of 2012, a federal judge in Washington, DC ruled that the US Food and Drug Administration (FDA) had broken the law in allowing certain states to bypass regulations and import unapproved drugs to be used in -executions. In his ruling, Judge Richard Leon wrote that the FDA had "acted in a manner contrary to the public health... [and] appears to be simply wrapping itself in the flag of law-enforcement discretion to justify its -authority and masquerade an otherwise seemingly callous indifference to the health consequences of those immediately facing the executioner's needle. How utterly disappointing."

It was like a tactical game, with events seeming to favour the abolitionist movement. It was the execution states' move. This is where the story takes a more -sinister turn; where it's no longer a game of cat and mouse with suppliers and their adversaries. This is the moment the war over death-penalty drugs reaches the executioner's table.

The source of drugs became shrouded in secrecy. In September 2013, it looked like death-row prisoner Arturo Diaz would become the first person to be put to death using pentobarbital obtained from a vendor that the Texas Department of Criminal Justice refused to identify. Then, a week before the execution it revealed it had obtained the drug from the Virginia Department of Corrections - at no cost.

In October 2013, stymied by human rights groups and defence lawyers working for the condemned, Florida decided to try something new - a never-before-tried drug in executions called midazolam, which is used by doctors to treat seizures and insomnia, and for sedating patients before medical procedures. Florida planned to use it first in its three-drug cocktail, followed by pancuronium bromide and potassium chloride. When it put convicted rapist and murderer William Happ to death in October last year, witnesses described how Happ shook his head back and forth while the drugs flooded his system. Two minutes later he opened his eyes, then yawned before his jaw dropped open. Lawyers for seven Florida death row inmates subsequently challenged the constitutionality of the drug.

Some states also turned to what are known as "compounding pharmacies" to obtain supplies. Unregulated by the FDA, compounding pharmacies primarily mix drugs for individual patients' needs - removing an ingredient that causes an allergic reaction, perhaps, or changing the form of the medicine from a pill to a liquid.

In October 2012, South Dakota executed Eric Robert - convicted of killing a prison guard - using pentobarbital it obtained from a compounding pharmacy. Following that, Georgia, Texas, Ohio and Missouri each announced they would secure pentobarbital from compounding pharmacies.

But critics said compounded pentobarbital wasn't regulated by the FDA, had much shorter expiration dates and if its potency was questionable it wouldn't sedate the inmate properly. "Mis-compounded pentobarbital poses a grave risk of suffering and pain in violation of the Eighth Amendment, as well as federal and state law," one attorney wrote in a lawsuit against an Oklahoma pharmacy.

Herbert Smulls, an inmate on Missouri's death row, was scheduled to die on 29 January 2014 using compounded pentobarbital. In a letter sent a week before to the FDA, Smulls' attorney, Cheryl Pilate, described information she had received that she said proved a compounding pharmacy sent the prison syringes filled with pentobarbital and had directed the Missouri Department of Corrections to store it at room temperature. An affidavit from a pharmacologist said improper storage of the pentobarbital at room temperature created a risk that Smulls could be "injected with a degraded, contaminated drug, thus causing excruciating pain".

If you're given a large enough dose of pentobarbital prepared under FDA supervision, most anaesthetists agree that you'll fall asleep and won't wake up, and although nobody knows exactly how it feels to be killed with pentobarbital, most agree it's probably painless. But compounded drugs might not be sterile. And because of the Hippocratic oath, medical doctors don't administer it to death-row inmates; it's injected by people who work in the prison.

As one anaesthetist I spoke to told me, "They don't know what they're doing. And so the pentobarbital can burn or cause pain on injection. And sometimes [inmates] are not given enough."

According to Mike Brickner, policy director for the American Civil Liberties Union (ACLU) in Ohio, compounding pharmacies have sold expired drugs or drugs that have not been stored properly. In 2012 a batch of contaminated steroids from a compounding pharmacy caused 750 people to fall sick with fungal meningitis. Sixty-four people died in that outbreak.

Late on 28 January, the supreme court granted Smulls a stay of execution, but it was lifted the next day and Smulls was put to death using the compounded drug.

By now, some states had begun talking about bringing back earlier methods of execution: Chris Koster, Missouri's attorney general, suggested it might revert to the gas chamber; Dustin McDaniel, the attorney general of Arkansas, hinted at a return to the electric chair. And in Wyoming, Republican state senator Bruce Burns even suggested firing squad as an alternative. "I consider frankly the gas chamber to be cruel and unusual," Burns told the Associated Press, "so I went with firing squad because they also have it in Utah."

The horror of what happened in Ohio on 16 January 2014 was palpable. Nobody could sugar-coat what they had seen: not the witnesses sitting in front of the glass screen; not the corrections officers standing guard; nor the prison warden whose job it was to stand next to the condemned man, Dennis McGuire.

Rather than source compounded pentobarbital from a US pharmacy, Ohio tried a new drug protocol on McGuire, convicted of the rape and murder of a pregnant woman in 1989. The cocktail would consist of the sedative midazolam and hydromorphone. But the combination was untested. Before the execution, David Waisel, associate professor of anaesthesia at Harvard Medical School who served as an expert witness for McGuire in his appeal, warned it could cause the condemned man "agony and horror", but Ohio went ahead regardless.

Witnesses said it took McGuire 26 minutes to die - the longest by lethal injection in the state's history. "My dad began gasping and struggling to breathe," said McGuire's son, in a press conference afterwards. "I watched his stomach heave, I watched him try to sit up against the straps on the gurney. I watched him repeatedly clench his fists. It appeared to me he was -fighting for his life but suffocating. The agony and terror... lasted more than 19 minutes."

David Waisel told me that McGuire was never sufficiently anaesthetised. "He was sitting there fighting to breathe for a long time, so the drugs did not work as the state proposed they would."

In more than a decade covering the death penalty in Texas, I'd interviewed scores of inmates at the Polunsky Unit, the concrete fortress in the east Texas town of Livingston that houses the state's death row wing. But I'd never witnessed an execution.

Several years ago, the criminal justice department's then-public information officer asked if I'd like to, but I didn't feel it would add anything to the stories I was writing.

With new drugs being tried, others obtained from questionable sources, and horrific stories of suffering on the gurney, I felt I needed to see what 35 states were doing in the name of the American people. The next person scheduled for execution in the US was Kenneth Hogan who was set to die by a cocktail of pentobarbital, the muscle relaxant vecuronium bromide, and potassium chloride on 23 January. Two weeks earlier, pentobarbital from the same batch, sourced from a compounding pharmacy, had been used to kill Michael Lee Wilson, who said he felt his entire body burning.

Hogan had been convicted of stabbing his friend to death in 1988. One morning that January he told his wife he was going to work, but instead went to see 21-year-old Lisa Stanley while her husband was out. The pair smoked marijuana and Hogan claimed Stanley tried to persuade him to steal a stereo system for her.

When he refused, they began to argue. According to court documents from Hogan's clemency appeal, she threatened to call his wife and tell her the couple were having an affair.

The row escalated. Hogan is quoted as saying "she went into the kitchen and she come [sic] back out... I was putting my coat on and she just pushed it [a knife] right at me. I didn't know what to say, do or think, I just grabbed the knife and it hurt, it hurt..."

He then describes killing Stanley with the same knife. "It was like I wasn't even there," he said. "Just somebody else... it wasn't even me. It was stabbing her and I couldn't stop him."

Prosecutors said Hogan stabbed Stanley more than 25 times in her back, neck and chest, after which he knocked over objects in her apartment to make it appear like she had been robbed.

Where GQ's Alex Hannaford witnessed the execution of Kenneth Hogan on 23 January 2014 © Rex / Shutterstock

It's -4C outside on the day I arrive in McAlester, a city of 18,000 people in southwest Oklahoma. The town gets its name from JJ McAlester, the state's -one-time lieutenant governor who was immortalised in the novel True Grit. Its biggest employer is the army's ammunition plant, which has the distinction of making all the bombs used by the US military.

The Oklahoma State Penitentiary is known locally as McAlester or Big Mac. An imposing white building with peeled paintwork, it became operational in 1908 and is mentioned in the opening scenes of John Steinbeck's novel The Grapes Of Wrath; his central protagonist Tom Joad is paroled from McAlester before setting out for California to escape the Dust Bowl during the Great Depression.

Big Mac is also famous for a prison riot in 1973, regarded as the worst in US history. It's also home to the state's death row, and that's where I go at 4pm on 23 January, to watch Kenneth Hogan die.

Jerry Massie looks like he could have been a film star. He wears a grey suit, shiny black shoes and his grey hair is neatly parted and glistens under the strip light. He has piercing blue eyes and a suntan. Massie is not a movie star. He used to be a probation officer in Oklahoma, but for years now he's been the head of public information for the state's department of corrections. If you're a journalist and you need to witness an execution, Massie's your man.

It's now about -6C and the sun is sinking low in the sky. An icy wind whips around the trees outside and a train whistles in the distance as it passes through. The media waiting room is a small tan building about 100ft or so away from the perimeter wall of the prison. Next to it is a patch of browning grass with a children's swing and some picnic benches - apparently for low-risk inmates from the minimum security unit down the road to meet their families.

Inside, the chairs, each with red plastic seats, face towards the front of the room where there's a desk, behind which sit two other prison staff. There's coffee and cookies provided for media witnesses, although today there will be only two members of the press here.

Massie hands me a sheet of paper. It says Hogan's last meal was given to him between 12.30pm and 1pm. He ate a cheeseburger from Braum's, a fast-food chain; a 10oz block of sharp cheddar cheese; large French fries (cooked crispy); a 500ml bottle of Pepsi; 15 packets of ketchup; and a bag of BBQ corn nuts.

Massie tells me he thinks the last meal forms part of the ritual inmates go through. "That's why you never get them causing trouble on execution day," he says. "They don't struggle on the gurney.

They want to go out like a man." Massie says he thinks they're resigned to the fact they're going to die on a certain day at a certain time and that they've made their peace.

Shortly after 4pm, Justin Juozapavicius, a reporter for the Associated Press, enters the media room. A jovial man in his thirties, Juozapavicius is about to cover his tenth execution.

Massie has "facilitated" media witnesses for about 190 executions in Oklahoma but he's never seen one himself.

At about 5.50pm, the phone will ring. On the other end of the line will be a prison staff member telling Massie the execution is about to begin and that we're to be taken to death row. While we're waiting, Massie tells me the story of one inmate, Robert Brecheen, who in 1995 overdosed on sedatives a few hours before his execution. He had to be rushed to hospital to have his stomach pumped before he was driven back to the prison only to be executed in the morning. "It was the same doctor who pumped his stomach that later pronounced him dead in the execution chamber," Massie says.

Even though I'm anticipating it, when the phone eventually rings it startles me. Massie's colleague picks up her keys from the desk and leads me and Juozapavicius to a waiting car. She drives us round the back of Big Mac, past the huge entrance to the old prison rodeo where inmates used to ride bulls and horses to crowds of paying spectators but which doesn't take place any more due to cutbacks. Next to that is what looks like a grey concrete bunker.

We're rushed inside. "No pat-downs today," says the large guard at the entrance. "Do you have cell phones on you?" We both say no and he hands Juozapavicius and me a notepad and pencil each before an officer escorts us inside the warm fortress, down a long hallway, and past a row of small barred windows.

The corridor narrows and we're told to go inside a small room with a yellow door. Twenty-four hours ago, Hogan was moved to a special holding cell, just feet from the entrance to the death chamber. He was allowed to shower and given a new set of clothes.

That's where he ate his last meal, made his final phone calls and met with a priest. By the time Juozapavicius and I take our seats, Hogan is already strapped to the gurney on the other side of the curtain and has IVs in his arms.

Two speakers attached to the wall above the window will broadcast his final statement. Behind me is another pane of one-way glass. Behind it sit eight relatives of Hogan's victim.

The two men who have been standing near the door with separate telephones pressed to their ears - one to the governor's office, the other to the warden in the execution chamber - replace the handsets. There has been no last-minute stay.

Once the curtain rolls back, the condemned man mumbles something and the warden tells him to take a deep breath in order to get his words out. Hogan acknowledges his family and friends, including the man in the cowboy hat, who sits in front of me. "I'm guilty of what I'm here for," he says, "and I take full responsibility for my actions. And to Lisa's family I say I'm sorry that I can't undo it.

I'm sorry to my family for all the pain and shame I've caused them.

Minister you've helped me to be a better believer and I thank you for that."

He tells everyone he loves them and when he finishes, the warden says, "Let the execution begin," and Hogan begins whispering what sounds like a prayer. He tilts his head up, looks at his family one final time, then lays back down, staring at the ceiling before closing his eyes. "There's a chemical taste in my mouth," he says. Then, "I'm going. I'm going. I'm going." Hogan takes his final breaths and I can just see the white sheet covering him blowing in the breeze of a small fan on the floor at the foot of the gurney. In seconds, Hogan's face turns from pink to grey.

Six minutes from when the execution began, the warden asks the doctor to check Hogan's vital signs. The doctor emerges from near the foot of the bed where he's been crouching, places a stethoscope on Hogan's heart and listens. He removes it, lets it dangle from his neck, then looks at the clock. "Time of death: 6.13pm," he says.

The warden, hands clasped behind her back, looks at Hogan's face. It's the last thing I see before the curtain closes. Hogan's family and friends wipe away tears. When we file out of the witness room, the two boxes of tissues remain untouched.

Back in the media room, Massie hands me two handwritten notes from the mother and father of the victim, Lisa Stanley. "In the 26 years since my daughter's death, Kenneth has not made any attempt to contact me nor any member of my family. He has shown absolutely no remorse for his actions," Norma, her mother, had written. "My daughter was a beautiful young woman with a heart of gold."

Her father, George, wrote that Hogan's execution would "not bring her back nor will it change the harm brought to our family.

But for 26 years, it has kept the horror of her death fresh in our memories. At last this will end the process."

The headquarters of the British pharmaceutical company in Acton, London, which, following the shortage of sodium thiopental in the US, began supplying departments of corrections with the drug for use in executions © Rex / Shutterstock

Closure. For two-and-a-half hours, as I drive from McAlester, Oklahoma, to my sister-in-law's house in Dallas, Texas, I wonder about this concept. Will Lisa Stanley's family really feel at peace now her killer is dead? I see Hogan's face in my mind, turning from pink to ash, a life snuffed out before my eyes.

Oddly enough I feel a certain amount of guilt. I feel, like everyone there, that I have been complicit in this macabre drama.

Media witnesses are part of the process - or as Massie had put, the eyes and ears of the public - while the state carries out its role.

A few days earlier I'd read a story by Kelly Kurt, a writer from Tulsa, Oklahoma, reflecting on her experiences as a former

Associated Press reporter. Kurt witnessed 16 executions up at Big Mac, but not once, she wrote, had she heard a condemned man cry. I don't know what difference it makes, if any, but Kenneth Hogan had cried: before he'd apologised to his victim's family, he'd wept on the gurney.

Kelly Kurt witnessed 16 executions up at Big Mac, but not once, she wrote, had she heard a condemned man cry.

Towards the end of April, two men were scheduled to die on the same evening on the same gurney where I'd watched Hogan succumb to a lethal cocktail of drugs. It was to be the first double execution in Oklahoma since 1937, but convicted killers Clayton Lockett and Charles Warner were to be put to death using a drug protocol that was new to the state: the sedative midazolam, followed by vecuronium bromide and potassium chloride.

Florida had used the three in succession before, but with a much larger dose of midazolam. The drug had also been used in the execution of Dennis McGuire in Ohio - in which his stomach heaved and he'd struggled for breath for 26 minutes before expiring.

Warner and Lockett's attorneys challenged the secrecy of this new source of lethal injection drugs. They won at the district court, but an intervention by the state's governor Mary Fallin caused it to reverse its decision.

At 6.23pm on Tuesday 29 April, media witnesses watched as Lockett was injected with the first drug - 50mg of midazolam in each arm. Eight minutes later, after a doctor checked his pupils, the prison's warden, Anita Trammell, declared, "Mr Lockett is not unconscious."

According to Ziva Branstetter, a journalist witnessing the execution for the Tulsa World newspaper, 13 minutes later Lockett kicked his leg and rolled his head to the side before mumbling something unintelligible. His body began "writhing and bucking", Branstetter wrote.

Two minutes later he began "grimacing, grunting and lifting his head and shoulders entirely up from the gurney... rolling his head from side to side." After that, the curtains separating the gallery from the chamber were drawn and the men and women who had watched the horrifying, failed execution were escorted from the room.

Later, they were told that 43 minutes after the first drugs were administered, Lockett died of a cardiac arrest. Unsurprisingly, Charles Warner's execution was stayed. But what media outlets were calling Oklahoma's "botched execution" had become international news. Even the White House said it "fell short of humane standards".

For her part, Oklahoma's Governor Fallin announced an inquiry.

Still, she was a staunch defender of the law. "[Lockett] had his day in court," she explained. "I believe the legal process worked.

I believe the death penalty is an appropriate response and punishment."

Originally published in the August 2014 issue of British GQ.