Johnathan A. Doody, who was born in Thailand and emigrated to the US, was 17 when he was accused of participating in the slayings at the Wat Promkunaram.
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.
Doody's second trial resulted in a mistrial in October after jurors failed to reach a verdict. His third trial ended with a conviction in January on nine counts of first-degree murder and 11 armed robbery and burglary charges.
Doody has maintained his innocence.
Sentencing is set for Friday morning in the United States. He faces multiple life sentences.
The verdict brought an end to a bizarre case that saw three trials over about 20 years on the same charges.
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 US$2,600 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 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 attorneys argued Garcia was 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 crime.
Prosecutors said both men were equally culpable and that Garcia had no reason to fabricate his story.
Doody's attorneys plan an appeal.
While Doody's confession that he went to the temple with Garcia but was outside when the shootings occurred helped seal his fate during his first trial, prosecutors were barred from using it at his retrials, given the ruling by the 9th US Circuit Court of Appeals overturning his conviction.
They instead relied largely on Garcia's testimony.
Doody was spared the death penalty in his first trial.
Prosecutors couldn't seek the death penalty in his retrials because of a 2005 US Supreme Court decision that prohibits authorities from pursuing that punishment against defendants who were younger than 18 years old when the crime occurred.