Authorities have arrested a third teenager in the killing of a 79-year-old church volunteer found dead in her Willmar home earlier this week. A 17-year-old boy from Willmar was arrested for the woman’s death early Thursday afternoon after a 19-year-old man and a 16-year-old boy were arrested late Wednesday on suspicion of murder and burglary in the slaying of Lila Warwick. Both of the first two suspects are also from Willmar, and remained in custody Thursday pending formal charges. Preliminary autopsy results show Warwick had multiple stab wounds and neck injuries that were consistent with strangling. She was found Monday when authorities conducted a welfare check on her. Investigators do not believe the killing was random.