Highway 12 was closed for more than six hours in both directions while Fairfield police investigated the incident.
"I heard her screaming like she's in pain," said witness Cherrie Heimsoth.
Heimsoth says first she heard loud banging noises, then screams coming from a nearby apartment complex. When she looked outside, she saw a man alternately punching and stabbing a woman near the lawn area.
"She was screaming so loud like it's her last, last breathe or whatever. And then she was in really, really pain when she's screaming. So like, somebody's hurting her," said Heimsoth.
Several witnesses called 911 but when police arrived the suspect with the knife ran off into the neighborhood.
A short time later, police confronted the suspect nearby on Highway 12.
"The suspect turned and attacked the officers with a knife and the suspect was subsequently shot. The officers then rendered first aid to the suspect," said Sgt. Matt Bloesh of the Fairfield Police Department.
The woman was airlifted to a local hospital with life-threatening stab wounds. She is in critical condition with nearly three dozen stab wounds. The suspect, Deonte Traylor, described by neighbors as the woman's boyfriend, later died from his injuries.
Authorities reopened Highway 12 just after 4 p.m.