A man charged with killing nine people, including six monks, at a suburban Phoenix Buddhist temple in 1991 carefully planned the slayings.
He didn't miss a shot as he fired 17 rounds into the victims, most to the back of their heads, a prosecutor told jurors in closing arguments on Monday.
Defence lawyers countered that the case against their client was flimsy, based solely on the words of a convicted murderer who was spared the death penalty in the killings in exchange for his testimony against Johnathan Doody.
Doody was 17 when he was accused of participating in the slayings at the Wat Promkunaram temple.
He was found guilty in 1993 and sentenced to 281 years in prison. But an appeals court threw out his conviction in 2011 after ruling that investigators improperly obtained his confession.
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His second trial ended in October with a mistrial after jurors failed to reach a verdict.
Doody's third trial began December 4. He has maintained his innocence.
"This was someone who planned out what was going to happen before he even stepped foot inside that temple," prosecutor Jason Kalish told jurors.
"This is somebody going person to person and back again killing them, shooting them, making sure they were dead."
Allesandro "Alex" Garcia pleaded guilty in the case and was sentenced to life in prison in exchange for his testimony and a promise that prosecutors wouldn't seek the death penalty.
During the retrials, Garcia described for jurors how the crime was Doody's idea, aimed at stealing about $US2600 ($A2,880) cash and valuables from the monks.
Garcia said he tried to persuade Doody not to kill the victims after the robbery, but Doody was determined to leave behind no witnesses.
Police eventually found the stolen items at Garcia's house, where Doody was staying at the time.
Doody's brother and mother were members of the temple, but neither were there the night of the shootings.
Defence lawyers say Garcia is lying and only implicated Doody to avoid a death sentence, pointing out for jurors how he initially implicated four other men from Tucson who were later found to have had nothing to do with the killings.
Authorities "were under a lot of pressure to solve these crimes," defence lawyer Maria Schaffer told jurors on Monday.
"The world was shocked by what happened with the murder of the monks."
