In the days leading up to the scheduled execution of Troy Anthony Davis, many questions have been raised about who or what institutions can stop the lethal injection planned for 7 p.m. today. Essentially, he has exhausted all avenues.

Q. Can the president grant clemency or stop the execution in any way.

A. No. While President Obama has said he thinks the death penalty does little to deter crime, he has no legal authority to get involved, officially, with a state execution. When the death penalty is  imposed for a state crime like murder, it is a state issue.

Q. Can the governor stop the execution?

A. No. Georgia's Constitution gives that authority only to the state Board of Pardons and Paroles.

Q. Can the Chatham County district attorney ask the judge who signed the death warrant to withdraw it?

A. Mike Mears, a professor at John Marshall  Law School and who has challenged the death penalty for decades, said probably not. "I don't think there is a legal mechanism to ask a judge for a do over," he said.

Q. Can the courts stop it?

A. Though his attorneys he can fill appeals, the only viable option is the Georgia Supreme Court and that is a questionable one. His lawyers would have to file in the Superior Court in Butts County, where the prison is located, and then, if necessary, the Georgia Supreme Court and then directly to the US Supreme Court. Federal law limits appeals in that court system and Davis has exhausted those.

Q. Can the Pardons and Paroles Board change its mind?

A. If additional evidence is provided the board could step in but the board has already twice rejected Davis' requests for clemency. This morning they said they would not reconsider additional requests.