The boy was facing a maximum 40-year sentence.
He and his then 12-year-old girlfriend were both accused of capital murder in the August shootings that led to the deaths of 46-year-old Darlene Nevil and her 48-year-old husband, Alan Nevil.
Dallas County chief public defender Lynn Richardson, who is representing the boy, says he can't comment on matters pertaining to juvenile offenders.
The girl, who is now 13, is set to go on trial in March.