Swedish authorities say the suspect in the Stockholm truck attack is known to have expressed sympathies with extremist organizations, including Islamic state (IS).
The 39-year-old man from Uzbekistan is suspected of having driven a truck into a department store in the city on April 7, killing four people and injuring 15.
Police said the suspect had been denied permanent residency in the Nordic country and was being sought by officials for deportation.
The man was named by Swedish media, but police declined to confirm his identity.
Meanwhile, reports said a second suspect had been arrested in connection with the deadly attack.
The person was arrested on "a lower degree of suspicion," Reuters news agency reported.
Thousands of people gathered in central Stockholm on April 9 for a vigil against terrorism.
No group has claimed responsibility for the attack.