I have fought and will continue to fight for clemency for all death row inmates until Virginia declares the death penalty unconstitutional.
Morva is scheduled to receive a lethal injection for the 2006 killings of Sutphin and Derrick McFarland, a hospital security guard.
"We urge the authorities to annul the death sentence against Mr. Morva and to re-try him in compliance with global standards related to due process and fair trial", they stressed.
The daughter of a Montgomery County deputy killed by William Morva is asking Governor Terry McAuliffe to halt his execution scheduled for Thursday, July 6.
Morva's attorneys have argued that he suffers from a severe mental illness that makes him unable to distinguish between delusions and reality.
The next morning, Morva shot and killed Sutphin who attempted to capture him.
Jailed in 2005 on accusations that he tried to rob a convenience store, Morva was taken to a hospital to treat an injury.
A court-appointed psychiatrist diagnosed Mr. Morva with delusional disorder in 2014, and noted that his crimes may have been committed as a result of the delusions he was experiencing.
William Morva's lawyers, Virginia state legislators, United Nations experts and even a daughter of one of his victims have all called for his planned execution to be stopped.
Dawn Davison, one of Morva's lawyers, said that he was in the grip of a powerful psychosis at the time of the killings and that jurors had not been told that he could be restored to health with treatment. "I just want justice for my son", Sutphin told The Roanoke Times on Wednesday.
Slain sheriff's deputy Eric Sutphin's family is divided over the fate of his killer, William Morva, who is set to be executed Thursday.
-Hungarian citizenship, and the European Union and the Hungarian embassy in Washington had called on McAuliffe to spare his life.
"We are concerned at Mr. Morva's deteriorating psychosocial condition", U.N. Special Rapporteurs Agnes Callamart and Dainius Puras said in a statement Wednesday.
"Mr. Morva's petition for clemency states that he suffers from a delusional disorder that rendered him unable to understand the consequences of his actions".
The U.S. Supreme Court declined in February to hear Morva's appeal.
Governor McAuliffe's spokesman Brian Coy said in an email that the governor "takes a decision like this very seriously and that he is careful reviewing all of the materials in this case".