Anthony Oyster was killed and Linda Oyster is currently listed in critical condition, Frasier told reporters.
Nicholson allegedly drove to the Herbal Choices Marijuana Dispensary and shot and killed resident Jennifer L. Davidson, 47, according to investigators.
Nicholson was caught on surveillance cameras at a sporting goods store picking up ammunition following the incidents and police later found the truck crashed and set on fire.
"Words fall short of describing the tragedy that took place on Friday and we are all left incredibly shaken," North Bend Mayor Jessica Engelke said at the news conference.
Later Sunday evening, the Springfield Police Department revealed more details on how Nicholson got to the Midwest.
Laura Johnson of Springfield was reported missing on Friday. Investigators said that Nicholson contacted her and forced her to drive north, the police said.
Dennis Johnson, Laura Johnson's father, told ABC affiliate KEZI that investigators told him the suspect approached her vehicle with a gun.
'They said she was forced to drive 33 hours to where they're at. She was able to talk him into turning himself in," Dennis Johnson told the station.
The Springfield Police said that Laura Johnson is safe and unharmed and on her way back to Oregon.
Frasier said that the investigation is ongoing, and the motives behind Nicholson's alleged actions are still unclear, according to Frasier.
The DA said he will file an extradition order and the suspect is slated to appear in a Wisconsin court this week. Frasier said Nicholson has been charged with 10 criminal counts, including six counts of murder in the first degree.