Two women died and eight people were wounded in what police said at the time they suspected was Finland's first terrorism-related assault.
The main suspect, who remains in custody, has been named as Abderrahman Mechkah, an 18-year-old Moroccan. He told a court he was responsible for the attack but denied his motive was terrorism.
Officers arrested a total of seven people after the attack, and have now released three of them without charge.