Among those executed in 2022 were "prisoners with serious mental illness, brain damage, intellectual disability, and strong claims of innocence," says Death Penalty Information Center.
One-third of the executions by lethal injection in the United States this year were "botched," a capital punishment watchdog group has said.
The Death Penalty Information Center (DPIC) said on Friday that 18 executions were carried out in the country in 2022, the fewest in a non-pandemic year since 1991.
"2022 could be called 'the year of the botched execution' because of the high number of states with failed or bungled executions," the nonprofit DPIC said in its annual report.
"Seven of the 20 execution attempts were visibly problematic — an astonishing 35 percent — as a result of executioner incompetence, failures to follow protocols or defects in the protocols themselves," it said.
In Alabama, for example, it took three hours to set an IV line for the July 28, 2022, execution by lethal injection of convicted murderer Joe James Jr., the DPIC said.
Two other execution attempts in Alabama were halted because of problems setting IV lines, and the governor ordered a moratorium on executions while a review of procedures is carried out.
What's New—DPIC 2022 Year End Report: Commutation of Oregon Death Row Headlines U.S. Death-Penalty Decline in a Year Marred by Botched Executions. https://t.co/h0RSpnvouV— DeathPenaltyInfoCtr (@DPInfoCtr) December 16, 2022
The DPIC said 37 of the 50 US states have abolished the death penalty or not carried out an execution in more than a decade.
The governor of Oregon this month commuted the sentences of all 17 inmates on the state's Death Row to life in prison.
This year there were five executions in Oklahoma, five in Texas, three in Arizona, two in Alabama, two in Missouri and one in Mississippi.
Among those executed in 2022 were "prisoners with serious mental illness, brain damage, intellectual disability, and strong claims of innocence," according to the DPIC.
"These cases would not even be capitally prosecuted today. "
It said the number of death sentences imposed was also on the decline, with just 20 so far this year.
In perhaps the most notable case, the young man who carried out the 2018 mass shooting at a high school in Parkland, Florida, was given life in prison after a jury declined to sentence him to death.
Public support in the United States for executing prisoners hovered this year just one percentage point above a five-decade low reached in 2021 when 54 percent of respondents told a Gallup poll they supported capital punishment.