Alamgordo, N.M. ? A jury on Tuesday convicted Cody Posey, 16, of murder and voluntary manslaughter for killing his father, stepmother and stepsister and hiding their bodies in a manure pile on Sam Donaldson’s southern New Mexico ranch in Alamogordo.

Posey, whose father Paul had been foreman on the ranch, hung his head and wept as the verdicts were read.

Defense attorney Gary Mitchell claimed the deaths were self-defense. Mitchell described years of physical and psychological abuse and said the flashpoint to the murders came when Paul Posey burned the boy with a metal welding rod after the teen refused to have sex with his stepmother the night before the slayings.

Posey could face life in prison on the first-degree murder charge. State District Judge Waylon Counts said an adjudication hearing would be scheduled within 30 days and remanded Posey into detention.