Evidence showed Dennis Wolter stabbed Kori Fredericksen more than 70 times, using five kitchen knives.
The Columbian reports that Wolter was formally sentenced Monday in Clark County Superior Court.
Prosecutors elected not to seek the death penalty because of Wolter's documented brain damage. That left life without parole as the only possible sentence.
At the time of her death, Fredericksen had a restraining order against Wolter and would have been a witness against him in a state criminal domestic violence case.