Relatives and activists say execution in Georgia should act as a wake-up call to US politicians to abolish the death penalty

In statistical terms, it may have been just another execution, a convicted murderer dispatched by prison medics with clinical efficiency. But, on the morning after the death by lethal injection of Troy Davis, there was no sign that the controversy over the case would be buried with him.

Davis was sent to his death despite a mass of evidence casting his 1991 conviction in doubt, including recantations from seven of the nine key witnesses at his trial for the murder of a police officer.

The execution has provoked an extraordinary outpouring of protest in Georgia, at the supreme court and White House in Washington, and in cities around the world.

Davis's case has become even more charged by the manner of his death: he was reprieved three times before Wednesday night and an intervention by the supreme court delayed the execution by four hours.

Relatives of Davis and civil rights leaders across the south vowed to fight on with the campaign to have the death penalty abolished.

Richard Dieter, the director of the Death Penalty Information Center, said it was a clear wake-up call to politicians across the US.

He said: "They weren't expecting such passion from people in opposition to the death penalty. There's a widely-held perception that all Americans are united in favour of executions, but this message came across loud and clear that many people are not happy with it."

Brian Evans of Amnesty, which led the campaign to spare Davis's life, said that there was a groundswell in America of people "who are tired of a justice system that is inhumane and inflexible and allows executions where there is clear doubts about guilt". He predicted the debate would now be conducted with renewed energy.

Martina Correia, Davis's sister, who kept vigil at the prison until the end, said that a movement had been formed that would transcend her brother's death.

Sitting in a wheelchair as she battles cancer, she said: "If you can get millions of people to stand up against this, we can end the death penalty."

The case has attracted high-profile backers, and the #RIPTroyDavis hashtag was trending on Twitter on Wednesday. Protesters with placards gathered outside the White House. But so far, national politicians have refrained from entering the debate.

Before the execution, White House press secretary Jay Carney said: "It is not appropriate for the president of the United States to weigh in on specific cases like this one, which is a state prosecution."

Rick Perry, the leading contender for the Republican nomination and a strong supporter of the death penalty, has made no public statement on the Davis case.

His presence in the Republican race guarantees that the issue of capital punishment will remain in the spotlight in a way it hasn't for years. At a TV debate earlier this month, the audience cheered when the host noted Texas had executed 234 death row inmates during Perry's time as governor.

In Jackson, Georgia on Wednesday night, there were dramatic scenes outside the Diagnostic and Classification Prison, where Davis was pronounced dead at 11.08pm.

About 500 protesters, most of them African-American, lined up on the other side of the road to the entrance of the prison which was barricaded by a cordon of Swat police dressed in full riot gear and brandishing tear gas rifles.

Davis was executed for the 1989 murder of Mark MacPhail, who was working off duty as a security guard when he intervened to help a homeless person being attacked. Davis was implicated by another man, Sylvester Coles, present at the time. But since the trial seven of the key witnesses have come forward to say their evidence was wrong, and others have testified under oath that Coles was the killer.

As he lay on the gurney, Davis once again declared his innocence, telling the family of MacPhail lined up behind a glass screen in front of him that the wrong person was about to die.

Raphael Warnock, the pastor of the Ebenezer Baptist church in Atlanta, where Martin Luther King had his ministry, said that though Davis's final hours were distressing, "through this, America is being transformed. This is one of those watershed moments when a human evil and injustice that is part of the norm suddenly becomes questioned and challenged."

Attention is now focusing on the American south. Though 34 of the 50 states still have the death penalty, only 12 states carried out executions last year, and now 80% of all executions take place in the south.

The south's history of racial segregation has also highlighted claims of racial bigotry. One of Davis's lawyers, Thomas Ruffin, has called his death a "legal lynching", pointing out that while black males make up 15% of the population of Georgia they fill almost half the cells on its death row.

The civil rights group the NAACP said it would step up its campaign to persuade states, particularly in the south, to abolish the death penalty. "States like Georgia have an ugly history of state-sanctioned executions like that of Troy Davis, and in our view they are reminiscent of the lynchings that happened in the deep south," said the NAACP's Steve Hawkins.

A further area of concern raised by the case is reliance on uncorroborated eyewitness accounts. Davis was convicted without any DNA or other forensic evidence, and the murder weapon was never found.

False witness evidence has been found to be a crucial factor in three-quarters of the cases where convicted prisoners were found to be innocent and were then exonerated. Al Sharpton, who attended the protests in Jackson, said he would be pressing for new legislation to ban death penalties in cases relying only on witness statements.

But it is unlikely that a new law overturning the practice could be passed in Washington. It is convention that individual states have control over death penalty rules, and the federal government can only lead by example in its own execution practices; it does not generally have the power to tell states like Georgia what to do.