(CNN) Arkansas put to death two men Monday night in the first back-to-back executions in the United States since 2000.

Jack Harold Jones and Marcel Wayne Williams were among eight inmates set for execution in April before the state's supply of a lethal injection drug expires at the end of the month.

The compressed timeline set off a series of last-minute challenges from inmates challenging the state's lethal injection protocol. The Arkansas Supreme Court and the 8th Circuit Court of Appeals denied requests for stays from Jones and Williams earlier Monday, as did the US Supreme Court.

Jones was administered the lethal injection at 7:06 p.m. Monday (8:06 p.m. ET) and pronounced dead 14 minutes later. Williams was administered the injection at 10:16 p.m. (11:16 p.m. ET) and was pronounced dead 17 minutes later.

Before Williams' execution began, a federal district court judge issued a temporary stay based on claims from Williams' lawyers that Jones' death was "torturous and inhumane." Infirmary staff tried unsuccessfully for 45 minutes to place a line in Jones' neck, before placing one elsewhere on his body, the emergency motion read.

The state called the claims "utterly baseless" and a federal judge lifted the temporary stay, clearing the way for Williams' execution to proceed.

These lethal injections were the first back-to-back executions in the United States since Texas carried out the death sentences of Brian Roberson and Oliver Cruz on August 9, 2000, according to the Death Penalty Information Center.

Arkansas' last double execution -- of Allen Willett and Mark Gardner -- was on September 8, 1999, according to the Department of Corrections.

'We hope this will help bring closure'

Jack Jones

Jones was convicted in 1996 of raping and murdering Mary Phillips in the accounting office where she worked as a bookkeeper.

She was strangled to death with a coffee pot cord while her daughter Lacey was tied to a chair. Jones beat and strangled Lacey, leaving her for dead. She regained consciousness as police photographers took pictures of the crime scene.

Searcy Daily Citizen reporter Tracy Whitaker said Jones appeared coherent as he delivered a two-minute statement focusing on Phillips' daughter, Lacey.

"It's a good thing that it's done, for her," Whitaker told CNN affiliate KARK

Lacey Phillips Seal thanked the governor and the attorney general's office in brief comments at a news conference.

"I'm glad that chapter is closed," she said Monday night.

The appeals court declined Jones' request for a stay based on his claim that the state's new lethal injection protocol will inflict cruel and unusual punishment.

"This evening the rule of law was upheld when the sentence of the jury for Jack Jones was carried out after 20 years of review. The victim's family has waited patiently for justice during that time. The jury sentenced Jack Jones to death, and his sentence was upheld by judges and reviewed thoroughly in courts of appeal at each level," Gov. Asa Hutchinson said.

"A governor never asks for this responsibility, but I accept it as part of the solemn pledge I made to uphold the law. Jack Jones expressed his willingness to proceed today, and we hope this will help bring closure to the Phillips family."

No visible signs of pain

Marcel Wayne Williams

Williams was convicted in the 1994 rape and murder of Stacy Errickson. He forced her into her car at gunpoint and made her withdraw money at several ATMs in transactions caught on camera. Her body was found two weeks later.

Williams argued that he would likely experience severe pain during the execution because of his medical conditions, and that the lethal injection amounted to cruel and unusual punishment. The 8th Circuit Court of Appeals denied him a stay based on that claim and another one arguing ineffective counsel in his trial.

A media witness said Williams' chest heaved as he laid on the gurney after receiving the sedative. There was no visible signs of struggle, such "grimacing" or "clenching of the fingers," KARK reporter Jessi Turnure said.

But she acknowledged there may have been pain she couldn't see.

"As far as we could tell, the inmate wasn't having any sort of trouble throughout it," she said.

How we got to this point

After Hutchinson signed their death warrants the eight inmates joined in a last-minute lawsuit challenging the clemency process. They argued the state's compressed schedule did not allow time for the state board to consider their cases. The 8th Circuit Court of Appeals denied them relief, and only one received a clemency recommendation.

The inmates also sued over the sedative used in the two-drug protocol. The lawsuit went to the US Supreme Court, which ultimately denied their motion for a stay.

The first execution was carried out on April 20. Ledell Lee became the first person put to death in Arkansas since 2005. He was convicted in 1995 of murdering a woman in her home two years earlier. He maintained up until his death that he was innocent.

Ledell Lee

Four are on hold pending appeal.

Lee's execution followed a flurry of court rulings Thursday, capped by the US Supreme Court's denial of multiple requests for stays of execution.

Amnesty International said it was a "shameful day," and that the state was treating people "as though they have a sell-by date."