DES MOINES (AP) — The death of a woman found fatally stabbed in a rural Iowa farmhouse near Early has been ruled a homicide, authorities said Monday.

Marilyn Schmitt, 45, was found dead Thursday in an upstairs bedroom of her home, about 100 miles northwest of Des Moines. An autopsy revealed she had been stabbed, Sac County Sheriff Ken McClure said in a statement. The criminal complaint says Schmitt was stabbed between 1:30 a.m. and 5:45 a.m.

Schmitt’s son, 21-year-old Kirk Riley Levin, has been charged with first-degree murder.