Jurors convicted a 16-year-old boy Tuesday of killing his family and hiding their bodies in a manure pile on newsman Sam Donaldson's ranch in southern New Mexico.

Cody Posey was found guilty of murder in the deaths of his stepmother and stepsister and voluntary manslaughter in the death of his father, who worked as Donaldson's ranch foreman.

Posey hung his head and wept as the verdicts were read, and defense attorney Gary Mitchell offered consolation by putting an arm on the teen's shoulder.

"I just held him like I would my own son," Mitchell said.

The jury, which heard three weeks of testimony, began deliberating on Monday.

Posey was arrested a few days after the bodies of his father and stepmother, Paul and Tryone Posey, and his 13-year-old stepsister, Mary Lee Schmid, were found on Donaldson's Chavez Canyon Ranch in July 2004.

Prosecutor Janice Schryer claimed that Posey's parents were loving, but said the youth didn't like ranch life and "took the opportunity to relieve himself of those expectations and that life."

Mitchell argued that the teen, who was 14 at the time of the slayings, was abused by his parents.

He 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.

On a videotape shown to the jury, Posey tearfully said he shot his stepmother first so she wouldn't call 911, then killed his father, then Mary Lee so she wouldn't tell on him.

Donaldson was the trial's first witness, taking the stand Jan. 17 to describe finding a bloody scene upon returning from a trip.

Posey could face life in prison on the first-degree murder charge in the death of his stepsister. State District Judge Waylon Counts said a sentencing hearing would be scheduled within 30 days.

Verlin Posey, brother of Paul Posey, told reporters outside the courthouse he was pleased with the verdict but disappointed the teen wasn't convicted of first-degree murder in his brother's death.

"I didn't like it, but I can live with it," he said.

Ellen Brust, whose son was married to Cody's biological mother, spent two weeks attending the trial. She offered her support for the boy.

"I know we'll be back and Cody will be vindicated," Brust said.