ATLANTA — Nathaniel Woods never pulled the trigger, but prosecutors said he was just as guilty as the man who did. He had been a mastermind, prosecutors said, luring police officers in Birmingham, Ala., into a house where three of them were killed.

A judge sentenced him to death, but as his execution neared on Thursday, Mr. Woods had a growing number of supporters arguing that there was no evidence showing he had plotted to ambush the officers.

Instead, his supporters claimed that Mr. Woods had been sent to death row based on a case rife with flaws and because of a practice in capital punishment cases that allows a defendant to be condemned without a unanimous jury decision — a practice that has been abandoned by every state but Alabama.

Mr. Woods was convicted in 2005, and at his sentencing prosecutors portrayed him as someone who hated the police. The officers’ widows said they believed that Mr. Woods ought to die, and all but two of the jurors agreed.