Troy Davis may be dead, but his execution Thursday in the American state of Georgia has made him the poster boy for the global movement to end the death penalty.

World figures, including Pope Benedict XVI and former U.S. President Jimmy Carter, human groups and commentators urged the execution to be halted — but to no avail. On Wednesday Davis was put to death by lethal injection for the 1989 killing of off-duty police officer Mark MacPhail despite doubts being raised over the conviction.

The execution sparked angry reactions and protests in European capitals — as well as outrage on social media. “We strongly deplore that the numerous appeals for clemency were not heeded,” the French foreign ministry said.

“There are still serious doubts about his guilt,” said Germany’s junior minister for human rights Markus Loening. “An execution is irreversible — a judicial error can never be repaired.”

The European Union expressed “deep regret” over the execution and repeated its call for a universal moratorium on capital punishment.

EU foreign policy chief Catherine Ashton said the bloc had learnt “with deep regret that Mr Troy Davis was executed,” her spokeswoman Maja Kocijancic told Agence-France Presse.

‘”The EU opposes the use of capital punishment in all circumstances and calls for a universal moratorium,” she said.

“The abolition of that penalty is essential to protect human dignity.”

Amnesty International condemned the execution in a statement.

“The U.S. justice system was shaken to its core as Georgia executed a person who may well be innocent. Killing a man under this enormous cloud of doubt is horrific and amounts to a catastrophic failure of the justice system,” Amnesty said.

In Britain’s Guardian newspaper, Ed Jackson, reporting from Jackson, Georgia, before the execution took place, gave 10 reasons why he believed the death sentence for “a man who is very possibly innocent” should be commuted.

Most of his argument concerned doubts about the conviction — seven of the nine key witnesses to the murder of MacPhail later recanted their evidence — but his final reason concerned the manner in which Davis was put to death.

“Even if you set aside the issue of Davis’s innocence or guilt, the manner of his execution tonight is cruel and unnatural,” Jackson wrote. “If the execution goes ahead as expected, it would be the fourth scheduled execution date for this prisoner. In 2008 he was given a stay just 90 minutes before he was set to die. Experts in death row say such multiple experiences with imminent death is tantamount to torture.”

In the right-of-center Daily Telegraph, Tom Chivers said the death penalty was “barbaric” and far more likely to be used against black people than white. But the main thrust of his argument was that there were serious doubts over the conviction.

“If you are pro-death penalty, you should be shouting twice as loud as the rest of us about the imminent murder of Troy Davis,” Chivers wrote. “Otherwise, you can’t claim to be supporting a stark but necessary act of justice. You’re just a fan of killing people in general. There are words for people like that. None of them are nice.”

On social media, many users predicted the execution would encourage a new civil rights movement to spring up. American novelist Hari Kunzru commented that on the issue of capital punishment the U.S. was isolated from much of the rest of the world “So I wake up to hear they executed Troy Davis. Wonder if most Americans realize how far out of step they are with international norms.”

And entertainer Vincent Tucker remarked that campaigners should continue their campaign despite Davis’s death. “It’s one thing to fight for Troy Davis when he was alive but the key question now is will you still fight for his cause after his death?”