Around the world and across the US, the firing squad execution in Utah has been met with a wave of criticism from those entirely opposed to the death penalty and those who say that shooting is not the most humane method of killing a prisoner.
In Salt Lake City, opponents held a multi-faith vigil. "I think we do not prefer to be associated with Iran, China, Saudi Arabia and the other countries who use the death penalty as we have used it," Nancy Appleby, chairwoman of the Utah Episcopal Diocese Peace and Justice Commission.
Rev Tom Goldsmith of the First Unitarian Church agreed: "Murdering the murderer doesn't create justice or settle any score." Bishop John Wester added: "The firing squad is archaic, violent and simply expands on the violence that we already experience from guns as a society."
Civil rights organisations in the US also joined the chorus of opposition. "Gardner's execution was both savage and inhumane and highlights the systemic injustices that plague the entire death penalty system in Utah and the rest of the United States," said John Holdridge, director of the American Civil Liberties Union. "Such arbitrary and discriminatory administration of the death penalty is the very definition of a failed system."
The USA has carried out 28 executions so far this year, and 1,216 since resuming judicial killing in 1977. Utah accounts for six of these executions.
Amnesty International, which has long called for a worldwide repeal of the death penalty, said shooting had also been used in China, Libya, Syria, Yemen and Vietnam this past year.
But that may no longer be the case in Vietnam. The day before Gardner was killed, legislators there voted to end the use of firing squad and make lethal injection the only method for executions. The change is due to take effect next year.
Vietnam has long been criticised for the number of death sentences if imposes. About 100 people are executed each year in Vietnam, many for drug-related crimes.
The decision to switch to lethal injection came after a parliamentary committee said it was necessary to find a more humane method.
Amnesty International said it "opposes the death penalty, in all cases and in all countries, regardless of the method used to kill the prisoner, or the nature of the crime for which he or she was sentenced to death."