Jurors must decide whether Paul Yum, 17, should be found not guilty by reason of insanity.

Yum, a freshman at Upland High School at the time of the shootings, pleaded not guilty and not guilty by reason of insanity. He was tried as an adult and could face 32 years to life in prison.

Next week, the same jurors who found him guilty will hear additional testimony and deliberate again to determine whether Yum was legally sane at the time of the killings.

Yum's defense attorneys have argued that the teen suffered from poor brain development and post-traumatic stress disorder as a result of family abuse.

"They have to prove that either he did not know right from wrong or he did not understand and appreciate the consequences of his actions," Deputy District Attorney Nancy Cooper said Friday.

If found not guilty by reason of insanity, Yum could be held in a state mental hospital for the rest of his life, or until doctors deem him safe for release.

Cooper has argued that the killings were premeditated and urged jurors to reach verdicts of first-degree murder.

Jurors deliberated for two days before finding Yum guilty of the lesser charges of second-degree murder.

Yum used his father's hunting rifle to shoot his mother, Esther Yum, 38, and sister, Christine Yum, 9, as they slept in the family's Upland home in June 1999.

A younger brother also home at the time was unharmed. The father, Tae Doo Yum, returned home from dinner with friends to discover the bodies of his wife and daughter.

After the shootings, Yum took thousands of dollars in cash from the home and drove his mother's Mercedes Benz to Las Vegas, where he was found days later and arrested.

Reach Tim Grenda at (909) 890-4460 or tgrenda@pe.com