If the pardon board shows no mercy to his plea for polygraph test on Wednesday, Troy Davis will be executed on Wednesday for a murder that he claims he did not commit.

The Georgia Board of Pardons and Paroles Tuesday denied a clemency appeal from Troy Davis, but his lawyer is hopeful that the prison officials and the pardon boards will let Davis take a polygraph test before his scheduled execution.

Davis is scheduled to be executed by a lethal injection at Georgia Diagnostic and Classification Prison near Jackson.

According to CBS News legal analyst Andrew Cohen, denial of clemency plea is routine.

Parole boards almost never grant clemency, so this is not a surprise, Cohen said. Now if Wednesday's execution is going to be halted, it's going to have to come from the federal courts, and the U.S. Supreme Court in particular, which last week halted a Texas execution.

Davis's supporters, including not only thousands of common people but also former FBI director, former president Jimmy Carter and Pope Benedict XVI, are trying all possible means to halt the execution. They have urged prison workers to go on a strike and even have considered a desperate appeal for the White House to consider Davis's innocence and halt the execution decision but as of now, the execution decision is on.

Davis is currently imprisoned for killing Mark MacPhail in 1989. MacPhail was an off-duty security guard in Savannah.

Last year, the U.S. Supreme Court granted an unusual opportunity to Davis to prove his innocence in the case but as his attorneys failed to do so, he is facing this execution on Wednesday.

Although Davis's attorneys claimed that he was convicted on the basis of flawed testimony, Justice was finally served for my father, the truth was finally heard, believed Mark MacPhail Jr., who was an infant at the time of his father's murder.