Authorities in Nebraska used the powerful opioid fentanyl to carry out a death sentence today, an unprecedented move.

It came as the state - which just three years ago saw lawmakers move to abolish capital punishment - completed a remarkable reversal and resumed executions for the first time in nearly a generation.

Nebraska experienced a series of firsts: the state's first execution in 21 years, its first lethal injection and America's first death sentence carried out with fentanyl, which has helped drive the opioid epidemic.

The execution was even more unusual considering the state's very recent history, which saw its legislature vote to abandon the death penalty in 2015 before voters reversed that decision the following year.

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At the centre of this was Carey Dean Moore, the 60-year-old inmate executed after spending more than half his life on death row.

Moore was sentenced to death for killing two Omaha cabdrivers in 1979. He said before the execution that he would not try to stop it, nor did he want anyone to intervene.

Nebraska had scheduled Moore's execution to begin at 10 am local time at the state penitentiary in Lincoln, the capital. The state's plan called for it to use four drugs, two of which prompted a recent lawsuit from a drug company arguing Nebraska was going to use its products. The company unsuccessfully asked a judge to block the state from using those drugs.

The first drug was injected into Moore at 10.24 am and the coroner announced his time of death at 10.47 am, corrections officials said.

Moore's case wound its way through the court system for nearly four decades, ever since the August 1979 slayings of Reuel Van Ness and Maynard Helgeland, both taxi drivers and Korean War veterans. Relatives of the men have said they were ready for an outcome in the case.

"Thirty-eight years has been long enough," Richelle Van Ness-Doran, Van Ness' daughter, recently told the Omaha World-Herald. "It's just prolonging this … it's like a slap in our face."

Nebraska corrections officials said Moore's execution was witnessed by four members of the news media, four people Moore chose to attend and one family member representing the victims.