(CNN) An Alabama man convicted of killing three police officers is lending his voice to defenders of Nathaniel Woods, a co-defendant who is scheduled to be executed Thursday for the same crime despite questions about his culpability.

Lawyers for Nathaniel Woods, 42, have maintained his innocence, pointing out that another defendant in the case, Kerry Spencer, confessed that he was the sole gunman in the 2004 slayings.

"Nathaniel Woods is 100% innocent," Spencer wrote from prison in a handwritten letter released this week by one of Woods' attorneys. "I know this to be a fact because I'm the person that shot and killed all three of the officers."

Woods' attorneys have asked Alabama Gov. Kay Ivey to commute his sentence. Woods is to be executed by injection on Thursday.

Ivey's office told CNN she will have no comment until a decision is made. There was no immediate comment from the state Attorney General's office.

Read More