By Matthew Bigg
ATLANTA (Reuters) - Defense lawyers mounted a final effort on Monday for Troy Davis, a Georgia man set to be executed on Wednesday for the murder of a police officer even though his supporters say he may be innocent.
The lawyers were due to present their evidence in Atlanta to Georgia's Board of Pardons and Parole, a five-person panel that will weigh whether to grant or deny clemency or issue a stay of execution of up to 90-days, his supporters said.
The case has become a cause celebre for opponents of the death penalty because seven out of nine witnesses on whose evidence Davis was convicted have since sworn affidavits recanting their trial testimony.
Nobel Peace Prize laureate Desmond Tutu and Helen Prejean, who wrote the book "Dead Man Walking," have issued statements on Davis' behalf.
Dozens of people on Monday held a prayer vigil in downtown Atlanta outside the building where the board was deliberating.
"The legal system has failed to provide an adequate safety net for a person with a serious innocence claim," said Laura Moye of Amnesty International USA.
A decision is expected later on Monday or on Tuesday and if the board declines to grant clemency it was unclear what other legal avenues his lawyers could pursue, said Anne Emanuel, a law professor at Georgia State University and an advisor to Amnesty.
Davis was convicted of the 1989 killing of police officer Mark McPhail near a Burger King in Savannah, Georgia. Since then he has been on death row and is due to be executed by lethal injection.
The case has been through a series of appeals and the U.S. Supreme Court took the rare step in August 2009 of ordering a new hearing for Davis to assess what his lawyers said was new evidence showing his innocence.
The justices transferred the case to a U.S. District Court in Georgia for a hearing and determination of his claims that new witnesses will clearly establish his innocence. A year later, the judge, William Moore, rejected Davis' claims of innocence.
(Editing by Greg McCune)