Williams was sentenced to death in 2000 for fatally shooting a former deputy warden during his 1999 escape from prison, where he was serving a life sentence for killing a college cheerleader the previous year. Kayla Greenwood emailed a statement to Williams through his attorney, telling him she had forgave him for the murder of her father.
For his final words, Williams appeared remorseful.
For his last meal, Williams asked to be served Holy Communion, and in his final statement, he apologized to the families of his victims he "senselessly wronged and deprived of their loved ones".
Williams' body violently lurched forward about three minutes after midazolam, the first of a three-drug cocktail, was injected at Arkansas' Cummins prison, an Associated Press reporter who was there said.
[Kenneth] Williams' body jerked 15 times in quick succession, then the rate slowed for a final five movements.
Hutchinson had put a temporary hold on Williams' execution Thursday evening to allow the US Supreme Court to consider motions for stays of execution.
Pool media reports show that after the lethal injection process began, Williams was shaking and appeared to be gasping for air.
Arkansas will have a more hard time obtaining additional lethal injection drugs after an unprecedented court challenge by a drug distributor and possible complications during at least one of the four executions the state carried out this month, experts said. Williams already was serving a life sentence for killing Dominique Herd, an 18-year-old cheerleader, when he escaped from prison, killed Boren at his nearby home and stole his vehicle, according to court records.
Republican Governor Asa Hutchinson has said the accelerated execution timetable was necessary because the state's stock of a sedative, midazolam, used in lethal injections will expire at the end of the month.More news: Husband charged with wife's murder as her Fitbit unravels his alibi
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Williams and several other inmates on death row originally fought their death sentences on the grounds that midazolam - the sedative used to render inmates unconscious - does not prevent a painful death. The American Civil Liberties Union of Arkansas also called for an investigation, arguing that the state may have violated the Eighth Amendment's prohibition of cruel and unusual punishment.
Arkansas routinely performs autopsies on executed prisoners, but results don't become available for four to six weeks. He was convicted in 1995 of murdering a woman in her home two years earlier.
All of the Arkansas inmates - including Williams - have died within 20 minutes of their executions beginning, a contrast from troubled midazolam-related executions in other states that took anywhere from 43 minutes to two hours. They had committed murders in the 1990s.
The state resumed executions in January 2015 with the lethal injection of Charles Warner and was just moments away from executing another inmate, Richard Glossip, in September 2015 when it was determined the wrong drug was delivered to the prison for Glossip's execution.
The governor said he does not think Arkansas needs to change its execution protocol, citing court rulings that have upheld the use of midazolam, which has also been used in flawed executions in other states.
If states can't get supplies of the three drugs needed for the lethal injection cocktail now used, authorities may have to switch to a one-drug lethal injection and use drugs such as sodium thiopental and pentobarbital.
Company representatives have said they have contracts with manufacturers saying they can not sell the drugs for executions. Turn the other cheek, forgive those who trespass against us, pray for those who persecute us, those are all Divine orders.
There are no more scheduled death row executions in Arkansas at this time. In a last-minute court filing, Williams' attorneys said he should receive a stay because the Greenwood family was not notified of his clemency hearing last month, but a federal judge rejected that request Thursday night. Afterwards, he continued to gasp and made an audible groaning sound until about 10:59 a.m., the witnesses said.
Witnesses watched the entire execution, and Wood could often be heard snorting throughout, even when the microphone was off.