He said he couldn’t call the crime a terrorist act until the assailant’s motive became clear.
The rampage at Crossroads Mall in St Cloud, about 100 kilometers northwest of Minneapolis, began shortly after 8pm on Saturday (Sunday AEST).
The assailant, who wore a uniform that resembled that of a private security officer, stabbed people in multiple positions before an off-duty police officer shot and killed him, Anderson said.
Eight people were taken to hospital with non-fatal injuries.
Anderson said police have no evidence to believe more than one person was involved in the attack.
Police had treated the individual on three previous occasions, but all for minor offenses, he said.