"The person is no longer a suspect," the prosecution authority said in a statement, providing no other details about the person nor the reason for the arrest or release.
Four people were killed -- including two Swedes, one Briton and one Belgian -- when the driver of a stolen beer truck mowed down pedestrians on a busy shopping street in central Stockholm on April 7.
Rakhmat Akilov, a 39-year-old Uzbek national, confessed to driving the truck and is being held in custody but investigators are still searching for possible accomplices.
The second unnamed suspect was arrested on Sunday and released late Tuesday.
No terror group has claimed responsibility for the rampage, which resembled vehicle attacks in Nice, Berlin and London.
Construction worker Akilov is a father of four who was refused permanent residency in Sweden in June 2016. He went underground last year after receiving a deportation order, police said.
He is known to have sympathies for jihadist groups, including the Islamic State (IS).
Eyewitness? Submit your stories now via social or:
Email: news@pulselive.co.ke
