Judge Mathis and the world on the execution of Troy Davis

"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."

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. source