(CNN) -- A child killer received a reprieve Friday from the Nebraska Supreme Court, which ruled that electrocution, the state's only means of capital punishment, is unconstitutional.
"Old Sparky" was used for 60 years to execute inmates in Texas before it was decommissioned in 1964.
Death penalty experts said the ruling is likely to put an end to a form of execution rarely used in the United States in recent years.
Lethal injection is administered in 35 of the 36 states that execute condemned prisoners, with Nebraska the sole exception.
"It is the hallmark of a civilized society that we punish cruelty without practicing it," said the ruling from the seven-justice majority. "The evidence shows that electrocution inflicts intense pain and agonizing suffering. Therefore, electrocution as a method of execution is cruel and unusual punishment."
The case involved Raymond Mata Jr., convicted of the premeditated murder of 3-year-old Adam Gomez in 1999. The Scottsbluff child, who was the son of Gomez's former girlfriend, was kidnapped, murdered and dismembered.
Adam's mother, Patricia Gomez, told a court at 2005 sentencing hearing that she supported execution. "He doesn't look remorseful and I feel no remorse for him," she told a three-judge state panel. "Death is what he deserves."
That panel reinstated Mata's capital sentence after the U.S. Supreme Court ruled in 2002 that death sentencing procedures used by Nebraska and other states were unconstitutional. The high court had ordered another look at Mata's appeal.
His lawyers had argued he had a tough childhood that contributed to his antisocial behavior.
The state high court ruling affirmed Mata's death sentence and made clear it is not abolishing capital punishment entirely, just the state's only means of execution.
The state justices said state procedures need to be revised if capital punishment is to survive further judicial scrutiny.
Electrocution, wrote the panel, "has proven itself a dinosaur more befitting the laboratory of Baron Frankenstein than the death chamber" in Nebraska.
Republican Gov. Dave Heineman said the ruling amounted to "judicial activism."
"I am appalled by the Nebraska Supreme Court's decision," he said. "Today the court has asserted itself improperly as a policy maker. Once again, this activist court has ignored its own precedent and the precedent set by the U.S. Supreme Court to continue its assault on the Nebraska death penalty."
Heineman's office indicated he will consider urging the legislature to replace electrocution with lethal injection. The legislative sessions ends in April.
Execution by electrocution has been used on 154 people in the United States since 1976, when the U.S. Supreme Court reinstated capital punishment. Figures from the Death Penalty Information Center note 929 people were executed by lethal injection during the same period.
"I think this is the final nail in the coffin for electrocution," said Richard Dieter, executive director of the Death Penalty Information Center, which opposes the capital punishment.
"Not many courts have given this kind of thorough review of a method of execution, and it will send a message to other states that capital punishment in general will be undergoing greater judicial scrutiny by state and federal courts," Dieter added.
The U.S. Supreme Court is currently considering a pair of cases from Kentucky over whether lethal injection is cruel and unusual punishment. The justices have imposed a de facto moratorium on executions since September while it reviews the constitutional questions.
Only three inmates in Nebraska have been executed since 1976, the last eight years ago. Nine men remain on the state's death row, including Jose Sandoval and Erick Velas, convicted for their roles in a notorious 2003 bank robbery massacre in Norfolk that left five people dead.
A state measure to abolish the death penalty entirely narrowly failed in the Legislature last year. Dieter noted state officials have long been considering whether to end executions, and that prevented a thorough review of the current electrocution protocols used by corrections officers. E-mail to a friend 
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