Defense attorney James Stokes said as the trial opened in Pensacola that co-defendant Rick Chavis, a 40-year-old convicted child molester, committed the murder on Nov. 26.
Prosecutor David Rimmer said Alex and Derek King beat their father, Terry King, 40, to death with an aluminum baseball bat and then set their rental home in nearby Cantonment, Fla., on fire to cover up the evidence.
Chavis was tried on the same charges last week, and Rimmer was the prosecutor in that trial too. The verdict was sealed, and all the verdicts will be read at the same time.
Alex and Derek King are standing trial together but will be judged separately by the jury three men, three women and four alternates, chosen last week.
The boys had originally confessed to the killing, but recanted during the Chavis trial, and said Chavis did it while they hid in the trunk of his car.
Chavis, whose home was a neighborhood hangout for teens, is accused of having a sexual relationship with Alex. Stokes said Terry King cut off contact between Chavis and Alex and that is why Chavis killed him.
But Chavis' attorney Michael Rollo turned the adult co-defendant's trial last week into a prosecution of the two boys, recounting their confessions and introducing several pieces of evidence damaging to their case.
The two boys are not eligible for the death penalty because of their age, and the prosecution said it will not seek the execution of Chavis.