Texas executed Lester Bower, one of the United States' longest-serving death-row inmates, who claimed that he was wrongly convicted of killing four men in October, 1983.

The Associated Press and ABC News reported that Bower received a lethal dose of pentobarbital Wednesday evening. He reportedly snored six times after receiving the injection, then stopped moving, and was pronounced dead 18 minutes later.

"Much has been said about this case," he said while strapped to the death chamber gurney, the AP reported. "Much has been written about this case. Not all if it has been the truth. But the time for discerning truth is over and it's time to move on."

Bower has spent more than 30 years behind bars appealing his death sentence. At the time of the incident, in 1983, Bower was a 35-year-old chemical salesman, and father of two who did not have a criminal record. The following year, Bower was convicted of shooting and killing four men in a hangar on a ranch near Sherman, Texas, 60 miles north of Dallas.

However, Bower maintained his innocence and was denied appeals to have his case reviewed with evidence that was previously withheld and could have potentially free him of any wrongdoing. He was the oldest and longest serving inmate on Texas's death row to be put the death.

"I do have remorse," Bower told The Associated Press. "I'm remorseful for putting my family and my wife and my friends through this."

"If this is going to bring some closure to them (the victim's family), then good. But if they think by this they're executing the person that killed their loved one, then that's going to come up a little bit short."

Despite that no witnesses or evidence were able to directly link Bower to the murders, and that the weapon used at the scene was also never found, Bower was convicted of killing Bob Tate, former police officer Ronald Mayes, sheriff's deputy Philip Good and interior designer Jerry Brown.

The prosecution devised a story that Bower was attempting to steal an ultralight aircraft that Tate was selling in 1983. Their case accused Bower of fatally shooting Tate, and that he proceeded to shoot and kill three other men who unexpectedly showed up at the hangar.

Bower's attorneys, however emphasized that there were many doubts surrounding their client's conviction. They claimed that Bower was convicted using circumstantial evidence, and that evidence has since surfaced that undermines the evidence that sent Bower to death row.

"This is a case in which there is a significant lingering doubt regarding guilt or innocence," Bower's attorneys insisted in a filing last week.

According to Bower's defense team, jurors did not have the opportunity to consider the fact that Bower did not have a previous criminal record. They also said that the 5th U.S. Circuit Court of Appeals used an incorrect legal standard in denying Bower an appeal a decade ago.

The Supreme Court decided against reviewing Bower's case in March, even though justices Stephen Breyer, Ruth Bader Ginsburg and Sonia Sotomayor said they would have tossed out his conviction. When the court refused to review the case, especially since key evidence was not presented in Bower's trial, Breyer wrote in the dissent "I recognize that we do not often intervene only to correct a case-specific legal error," he said. "But the error here is glaring, and its consequence may well be death."

On the day that the crime took place, Bower claimed he approached the ranch to buy an ultralight aircraft. At the ranch, he met Tate, Good and Brown. Bower says he paid $3,000 upfront for the plane. For the remaining $1,500 he owed, he wrote an IOU on a business card that he handed to Tate. Bower maintained that the men were alive when he drove away from the ranch.

Later that night, the police found the four men dead. Mayes was found dead at the entrance, the other three men lay dead inside the hangar. Investigators tracked down that Bower made calls to Good. Bower admitted that he had spoken to Good, but he lied out of fear, and denied that he had ever visited the hangar. At the time, Bower's wife was also against buying the aircraft.

"If I came forward, what might happen about the safety of my family? Then, of course, I had not exactly been truthful with my wife, so there was a level of embarrassment there, family-wise," Bower told Texas journalist Tim Madigan. "And once you kind of start a lie, it just kind of grows and it rolls along. It just consumed me."

Investigators found pieces of the aircraft at Bower's home months later. Bower was arrested, and convicted of the four murders. The Italian-made Fiocchi ammunition that was used to kill the four men was also extremely rare, according to prosecutors. Bower was linked to the crime scene since the state found evidence that Bower was one of the few people to purchase the ammo.

Years later, Bower's new team of attorneys, discovered that crucial evidence was never presented to the court and it was enough to prove that Bower did not carry out the murders. The $3,000 Bower paid Tate was never found, nor were the details of the business card mentioned. They also stated that the ammunition was not as rare as the prosecution made it out to be. Bower's defense team has since argued that the murders could potentially be the result of a drug deal gone wrong.

Prosecutors asserted that Bower has nothing new to add to his defense.

"Bower raises no new claim or claims, but merely seeks to re-open a judgment long since final," the Texas Department of Criminal Justice told the Supreme Court in May in response to an appeal.

Texas has already attempted to execute Bower six times. Bower was the second-longest Texas inmate on death row to be executed. Texas is one of the top five states in the US with the highest execution rates. Since 1976, Texas has executed 526 people, and 264 people are currently on death row. Before Bower, the state executed seven people this year, including Robert Ladd in January who had an IQ of 67.

Follow Arijeta Lajka on Twitter: @arijetalajka

The Associated Press contributed to this report.

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