At the start of the trial for the fivefold murder in Kongsberg, Norway, last October, the accused confessed to the crime.
The NTB news agency reported on Wednesday.
Equipped with a bow, arrow and stabbing weapons, the 38-year-old killed five people in the small town and injured three.
According to police, all of the fatalities were stabbed, most in their own homes.
Among the dead was a native German.
The man is said to have thrown a knife at three police officers.
The public prosecutor wants to demand the placement of the native Dane in a psychiatric institution.
According to the prosecution, the man was mentally ill during the crime in autumn 2021.
The prosecutors therefore consider him to be of unsound mind.