(CNN) Arkansas executed its fourth inmate in eight days, ending a frantic schedule as the state's supply of a sedative it uses in lethal injections expires at the end of April.

Kenneth Williams, 38, initially was sentenced to life in prison for the 1998 killing of Dominique Hurd, a university cheerleader. He was later convicted of capital murder after he escaped from prison in 1999 and killed Cecil Boren.

Boren's daughter, Jodie Efird, watched Thursday night's execution from the death chamber in Arkansas' Cummins Unit prison. She said Williams' death may not bring closure to her family, but it helps a little.

"Every time we drive down this road, he's not here anymore," she said of Williams.

Williams expressed remorse in his final words.

"I was more than wrong. The crime I perpetrated against you all was senseless," Williams said, according to CNN affiliate KATV-TV in Little Rock.

Williams died by lethal injection at 11:05 p.m. local time. He was one of eight inmates who had been scheduled to be put to death before Arkansas' supply of sedatives used in its lethal injections expires at month's end.

The expiration is an issue because a resupply is uncertain as Arkansas and other states struggle with suppliers that don't want their products used in executions . The sedative, midazolam, is a controversial replacement for anesthetics that Arkansas and other states can no longer obtain.

Four of the eight inmates have been executed, but the courts have postponed the other four executions for various reasons . Because of the delays, those four inmates will not be executed in April, a spokesman for Arkansas Gov. Asa Hutchinson said.

Hutchinson had put a temporary hold on Williams' execution Thursday evening to allow the US Supreme Court to consider motions for stays of execution. The court denied all the motions.

AP: Williams' body lurched

Williams' body lurched violently about three minutes into the execution, an Associated Press reporter who was there reported. That account led Williams' attorneys to demand an investigation and call the sedative into question.

JUST WATCHED Court rules on the use of lethal injection drug Replay More Videos ... MUST WATCH Court rules on the use of lethal injection drug 01:50

The body jerked 15 times in quick succession, the AP reported , before moving five more times at a slower rate.

Williams' attorneys singled out midazolam, the sedative that Arkansas and other states have used as a replacement for anesthetics that drug companies have withheld.

Midazolam, critics say, contributed to Death penalty critics have argued for years that midazolam is a sedative -- not an anesthetic -- and that the condemned would feel tortuous pain from the drugs that come next.Midazolam, critics say, contributed to botched executions in other states.

"The accounts of the execution of Mr. Williams tonight are horrifying," Williams' attorney Shawn Nolan said.

"We are requesting a full investigation into tonight's problematic execution," Nolan said.

The governor said in a news conference Friday he sees "no reason for any investigation other than the routine review that is done after every execution."

Wendy Kelley, director of the state Department of Correction, briefed Hutchinson after the execution. Hutchinson said that the movement seen by witnesses "was described as coughing without noise" and from Kelley's account, there was "no indication of pain."

Another witness, Little Rock TV anchor Donna Terrell, told CNN affiliate KARK-TV that after the midazolam was injected, Williams' chest started going up and down rapidly from 10:55 to 10:59 p.m.

After that, it appeared he stopped breathing, or it was no longer noticeable, Terrell said.

Even though the microphone was turned off, Terrell said, witnesses could still hear heavy breathing.

But Williams' face was expressionless, and it didn't appear as if he were in pain, she said.

A third witness, Arkansas state Sen. Trent Garner, said on Twitter that "the inmate did not suffer or seem in pain."

I witnessed the #ARexecutions ; the inmate did not suffer or seem in pain. His face was calm. It was not cruel, unusual, botched or torture. — Senator Trent Garner (@Garner4Senate) April 28, 2017

"His face was calm. It was not cruel, unusual, botched or torture," Garner's tweet reads.

The arguments over drugs

The eight Arkansas inmates -- like many before them across the country -- initially fought their executions on the grounds that midazolam does not reliably prevent a painful death and helped contribute to botched executions in other states. But the Arkansas Supreme Court denied the claim.

States generally didn't use midazolam in the past, but they've turned to it as drug makers clamped down on the use of other drugs in executions.

Lethal injection traditionally required a three-drug cocktail: The first (sodium thiopental or pentobarbital) put the prisoner to sleep; the second (pancuronium bromide) brought on paralysis; and the final agent (potassium chloride) stopped the heart.

But manufacturers and European countries started withholding sodium thiopental and pentobarbital around 2010, saying they didn't want them used in executions. Arkansas and other states turned to midazolam as an alternative.

In 2014, several executions, all employing midazolam, were widely considered botched. In Ohio, Dennis McGuire gasped and convulsed for 10 minutes before dying. In Arizona, Joseph Wood snorted and gulped for air as he died over a period of two hours. And in Oklahoma, Clayton Lockett writhed for 43 minutes before succumbing to a heart attack.

After each of those cases, states issued holds on capital punishment while the processes were reviewed.

It's unclear whether Arkansas will receive fresh supplies of midazolam after its current batch expires. One manufacturer, West-Ward Pharmaceuticals, filed a brief in support of the eight inmates this month, saying it tries to ensure its medication isn't used in executions.

The other executed Arkansas inmates

On April 20, Ledell Lee became the first of the four Arkansas inmates to be executed as well as the first person in the state in 12 years. He was convicted in 1995 of murdering a woman in her home two years earlier.

Jack Jones and Marcel Williams were then put to death Monday in the first back-to-back executions in the United States since 2000. They had committed murders in the 1990s

The executions have drawn international outcry.

"While the rest of the country and the world moves away from the death penalty, Arkansas has shown just how committed it is to running in the wrong direction," said James Clark, a senior campaigner at Amnesty International USA.

"While it is too late for Kenneth Williams, Jack Jones, Marcel Williams and Ledell Lee, it is not too late to commute the sentences of all of those remaining on death row."

Prison escapee

After his conviction in Hurd's killing, Kenneth Williams escaped from Cummins prison the following year and killed Boren at his home a couple miles away. He stole Boren's vehicle and drove to Missouri, where he was captured after causing a traffic accident that killed a driver, Michael Greenwood. He was convicted of capital murder for Boren's death in 2000.

"We just live 2 miles from the prison. ... Every time I go up and down the highway, I know he's there," Genie Boren told KATV

"We are looking forward to this happening so we can put it behind us."

Williams was executed at the same prison he escaped from 17 years after his conviction in Cecil Boren's murder.