A North County jury convicted Jason Duane Cooper, 27, of first-degree murder for killing his mother-in-law and teenage sister-in-law, stabbing them repeatedly in their Fallbrook home.
On Monday, it took the same jury less than an hour to find Cooper was sane when he committed the attack.
First-degree murder carries a sentence of 25 years to life in prison. The jury also found that Cooper was guilty of torture and multiple killings in the attack on April 26, 2006. Those special circumstances increase his punishment to life in prison without the possibility of parole.
Jenna Liebner, 16, was stabbed 56 times. Her mother, Robyn Liebner, suffered 27 stab wounds.
Cooper has admitted to killing his in-laws. He will likely spend the rest of his life in prison without the possibility of parole. Sentencing is set for July 9.
