Protestors display banners in the protest area at the Georgia Diagnostic and Classification prison where convicted killer Troy Davis is set to be executed by lethal injection in Jackson, Georgia September 21, 2011. [Photo/Agencies]

JACKSON, Ga.- The US state of Georgia executed convicted murderer Troy Davis on Wednesday in a case that drew international attention because of claims by his advocates that he may have been innocent.

Davis was put to death by lethal injection at 11:08 pm EDT/0308 GMT on Thursday at a prison in central Georgia for the murder of a police officer in 1989, prisons spokeswoman Kristen Stancil said. The execution was delayed by more than four hours as the US Supreme Court considered whether to issue a stay.

The case provoked protests and an online petition accumulated nearly a million signatures because of doubts expressed in some quarters over whether he killed police officer Mark MacPhail in 1989.

MacPhail was shot and killed outside a Burger King restaurant in Savannah, Georgia, as he went to the aide of a homeless man who was being beaten. MacPhail's family say Davis is guilty and his son witnessed the execution.

Since Davis's conviction, seven of nine witnesses have changed or recanted their testimony, some have said they were coerced by police to testify against him and some say another man committed the crime.

No physical evidence linked Davis to the killing.

Davis went to his death saying he was innocent, according to journalists who witnessed the execution.

"The incident that night was not my fault. I did not have a gun," Davis said, according to Rhonda Cook of the Atlanta Journal-Constitution newspaper.

"I did not personally kill your son, father and brother. I am innocent," Cook quoted Davis as telling members of MacPhail's family who were present in the death chamber.

Hundreds of protesters rallied outside Georgia Diagnostic and Classification prison earlier, chanting "I am Troy Davis" and other slogans and a cheer briefly went up when it was reported that the execution had been delayed.

But the crowd dwindled as the evening wore on, and by the time the execution took place they were outnumbered by police in riot gear. Most of Davis' supporters slipped away in silence as the execution was announced.

"This is a tragic moment. We were hoping for a different result," said Raphael Warnock, pastor of Ebenezer Baptist Church in Atlanta, whose church was once led by slain civil rights leader Martin Luther King.