Graham is due to die by lethal injection on Thursday, after being convicted of shooting a man dead in Houston in 1981.

Jesse Jackson has agreed to witness the execution

US civil rights activist Jesse Jackson has called on Texas Governor and Republican presidential candidate George W Bush to delay the execution because of doubts over the conviction.

Mr Bush has defended the use of capital punishment in Texas - where there have been 131 executions since he took office more than five years ago - "because I believe it saves lives".

Verdict doubts

Only one of six witnesses has identified Graham as the killer Gun found on Graham could not have fired the fatal bullet Four witnesses say Graham was elsewhere when the crime took place

The Texas Pardons and Paroles Board is due to make its decision on whether to proceed with the execution at 1330 local time (1830 GMT) - several hours before the execution is scheduled to take place.

Mr Bush was heckled by protesters at a fund-raising dinner in Los Angeles on Tuesday.

Opposition

"Bush says death row; we say hell no!" several dozen campaigners shouted outside the Century Plaza Hotel.

Protesters have been targeting Bush on his campaign trail

"I think it's important that they [voters] know that I'm going to make decisions based on the law and justice and fairness," Governor Bush said.

A law professor has said Graham, who now goes by the name Shaka Sankofa, was convicted with the least amount of evidence of 648 death penalty cases he had studied.

Majority in favour

Lawrence Marshall of Northwestern University School of Law in Chicago added that several witnesses said they had seen someone other than Graham at the scene of the killing, and that a new hearing should be held.

George Bush: "Law and justice and fairness"

Graham was 17 when convicted of the killing.

Support for the death penalty is running at over 60% nationwide.

But the BBC's Paul Reynolds in Houston says there is concern, prompted by the application of DNA evidence to old cases especially, that innocent people are being executed or are on death row.

Florida 'reprieved' dies

In Florida, a man who had won a reprieve 11 minutes before he was due to die was finally executed on Thursday.

An act of state-sponsored vengeance

Amnesty International on Provenzano's execution

Thomas Provenzano, 51, had been scheduled to die on Tuesday evening for killing a bailiff in 1984, but three Federal Appeal Court judges issued a stay of execution.

Their decision came as Provenzano was strapped to a chair with intravenous needles in his arm for poison to be injected. However, the judges reversed their decision the next morning and the execution was rescheduled immediately.