GENEVA (Reuters) - United Nations human rights experts appealed to the United States on Friday to impose a moratorium on the death penalty for federal crimes, including the sentence imposed on the Boston Marathon bomber, with a view to abolishing the practice.
Dzhokhar Tsarnaev, 21, was moved on Thursday to a U.S. penitentiary in Florence, Colorado, home to the so-called "Supermax" unit that houses high-risk prisoners.
The ethnic Chechen was transferred a day after a federal judge in Boston, Massachusetts, sentenced him to death by lethal injection for killing four people and injuring 264 in the April 2013 bombing and its aftermath with his late older brother.
"This decision contradicts the trends toward abolishing the death penalty in the country in law and practice," U.N. special rapporteur on executions Christof Heyns and U.N. torture investigator Juan Mendez said in a joint statement.
Tsarnaev's acts fall within the definition of "most serious crimes" to which the United Nations says the death penalty - if imposed at all - should be restricted.
More than three-quarters of countries worldwide have abolished the death penalty in law or in practice, the experts said.
There is "no proof" that the death penalty has a deterrent effect and many executions have resulted in "degrading spectacles", they added.
"Especially if imposed for crimes motivated by ideological or religious considerations, this form of punishment plays into the hands of those who treat life as dispensable and encourage rather than discourage them," their statement said.
Massachusetts abolished capital punishment for state crimes in 1984, it noted.
"The decision of a federal jury to impose the death penalty for a crime committed in Massachusetts, where the death penalty has been abolished for decades, illustrates how out of place this form of punishment is," the U.N. experts said.
Under international law a nation is accountable for all of its jurisdictions, according to Heyns and Mendez. "And there are concrete steps that the Federal Government could take, including a moratorium on the death penalty for federal crimes."
Mendez accused the United States in March of stalling on his requests to visit its prisons, where 80,000 people are in solitary confinement, and to interview inmates on his terms.
He has sought for more than two years to enter U.S. prisons, including maximum-security facilities, specifically ADX in Colorado where inmates include Oklahoma City bomber accomplice Terry Nichols, underwear bomber Umar Farouk Abdulmutallab and Unabomber Ted Kaczynski.
U.S. human rights ambassador Keith Harper told a news briefing on June 11 that talks were "ongoing" with Mendez regarding a "robust and effective" visit.
Harper, asked whether he expected the visit to take place this year, said: "We hope it will, yes."
Editing by Gareth Jones