PHOENIX -- One of three suspects accused of killing a South Phoenix man two years ago has pleaded guilty to second-degree murder and arson. Matthew Moreno, 21, is scheduled to be sentenced on July 9. Moreno and two other men were arrested in May 2010 on suspicion of first-degree murder, arson, kidnapping and burglary. Moreno, Adan Gonzalez and Booz Moreno allegedly beat and stabbed the victim, slit his throat and then set his house on fire in a deadly act of revenge.Authorities said the victim was killed because the suspects believed he was having an affair with Gonzalez's mother. In January, Booz Moreno was sentenced to life in prison after pleading guilty to first-degree murder and aggravated assault.