A northwest Iowa man is convicted of killing his stepdaughters as part of what prosecutors say was a Satanic ritual. The Woodbury County jury only deliberated a few hours before returning the verdicts against 26-year-old Lawrence Harris on Thursday afternoon.

Harris was found guilty on both counts of first-degree murder in the killings at the family home in Sioux City on January 6th of last year. Ten-year-old Kendra Suing and her eight-year-old sister, Alysha, were stabbed and strangled. The defense argued Harris was insane when the crimes were committed.

Prosecutors described the killings as a ritual that went bad. The conviction carries a mandatory life term. Formal sentencing will come February 18th.