Nathaniel Woods was pronounced dead at 9.01pm on Thursday.

He was killed by lethal injection in Alabama, one of 29 American states that still has the death penalty. The 43-year-old was convicted 15 years ago for being involved in the death of three police officers, all of whom were shot by Kerry Spencer.

Officers Carlos Owen, Harley Chisolm and Charles Bennett died at a drug house while serving a misdemeanour domestic assault warrant. Woods was accused of setting up the ambush that led to their deaths in 2004.

Chilsolm’s sister called the governor of Alabama, Kay Ivey, in a bid to stop the execution. “I do not think that Nathaniel is guilty of murder,” a statement from her said, according to Woods’ lawyer. “Please do not move forward with the hasty decision to execute Nathaniel. My conscience will not let me live with this if he dies. I beg you to have mercy on him.”

Many have pointed out repeat failings in the case of Nathaniel Woods who – although he pulled no trigger – was killed by the state. His story has gained traction around the world, with celebrities such as Kim Kardashian and Martin Luther King III decrying the decision.

Martin Luther King III asks for stay of execution for Nathaniel Woods

“Woods, a black man, was sentenced to death even though even the prosecutors in his case agreed he did not personally kill anyone,” Cassandra Stubbs, director of the Capital Punishment Project at ACLU, tells The Independent. “He was sentenced to death despite the fact that two of the jurors rejected a death sentence … Woods ​was repeatedly denied the quality of counsel that could and should have saved his life.” Alabama is the only US state where you can be sentenced to death if jurors don’t agree a verdict.

This is by no means an isolated incident. Since 1976, 1,515 people have died by the death penalty in America, and since 1973, more than 165 people have been released from death row with evidence of innocence. In certain US states a person can be sent to death row for commissioning or being an accomplice to a crime. “If you pick me up and we drive to a gas station and I go in and shoot the convenience person and get back in your car and you drive away, you can be held just as accountable for the murder of that person as I can,” Gregory Joseph of the National Coalition to Abolish the Death Penalty (NCADP) tells us.

Out of those 1,515 deaths, 1,337 have been by lethal injection. Several death row inmates in the US have opted for the electric chair over the infamous drug cocktail, the latter notorious for being a potentially horrific way to die.

The lethal injection – a combination of three drugs – has been widely condemned, with no American pharmaceutical companies willing to supply the drugs.

Robert Dunham, executive director of non-profit Death Penalty Information Centre – that is neither for or against capital punishment – explains to us how the lethal injection kills someone.

After decades of using gas chambers, hanging and the electric chair, states sought a less “gruesome” way to execute people, Dunham says, the thinking being it would be a “simple medical procedure where someone goes to sleep”.

“Studies now show this three drug process is the equivalent to waterboarding, suffocation and being chemically burned at the stake,” Dunham says. “The people who developed the drug weren’t aware of what it actually did to a person. It wasn’t developed by a doctor.”

The first stage of the typical three-drug protocol is to sedate the restrained prisoner; Midazolam being the current drug of choice. Next comes a drug such as rocuronium bromide to paralyse the muscles, then potassium chloride to stop the heart.

At one point during the execution of Woods he jerked his left arm upward against his restraints before his breathing slowed and eventually stopped, according to the Associated Press.

“Midazolam is not an inappropriate drug to be used for execution purposes,” Dunham says. “It’s a perfectly good medical drug, but it does not have the properties that would knock a prisoner out and keep them sedated so they don’t feel the effects of the other drugs.”

And what are those effects?

“You are drowning. You are aware of the fluid buildup and you are aware of the inability to get air in and expel the fluid,” Dunham says. “And while that happens you are being chemically burned – a chemical fire – and the combination of those things resulting in an extended period of a torturous death.”

As no pharmaceutical companies in America are willing to sell their medicines for the use of executions, states have had to find alternative means of acquiring them. For example, Ohio allegedly ordered Midazolam through its mental health department, then went on to transfer it to the Southern Ohio Correctional Facility, where the state’s death chamber is located. Or in the case of Nevada, where the pharmaceutical company Alvogen sued over claims their drug was supplied to the prison illegally.

Woods was the first person to be executed in Alabama this year. There are currently 173 inmates on death row in the state.

“Governor Ivey in Alabama has moved forward with all the executions that have come across her desk,” Joseph says. “She even authorised the execution of two people last year and the day before she signed a very restrictive abortion bill that pretty much made it illegal in the state and at the signing she said Alabama is a pro-life state – the next day she signed death warrants.”

The governor’s office did not reply to a request for comment.

Numerous studies show the death penalty does not act as a deterrent, and is not a cost effective punishment in the US. The case of Nathaniel Woods may be “accelerating” America’s rejection of capital punishment, Stubbs says. “​It’s time for this country to reject the discriminatory, inhumane, and error-prone punishment all together.”

Prosecutors have said Woods set up the ambush which caused the death of three officers. His supporters claim he received poor legal advice resulting in an inadequate investigation. Writing in an open letter, Spencer said: “Nathaniel Woods is 100 per cent innocent. I know that to be a fact because I’m the person that shot and killed all three of the officers that Nathaniel was subsequently charged and convicted of murdering.”