At a press conference on Tuesday, police said the man in custody, a Swedish citizen and 20 years of age, is a suspected accomplice in the shooting, which happened just before 10 am on Monday. He is also suspected of crimes against weapon laws and is known to the police.
Police have searched several houses and confiscated what they believe is the murder weapon. Police say there was a large number of witnesses to the shooting. Some have already spoken with officers, but more are encouraged to step forward.
Two other people were taken to hospital after the shooting. One is said to be the victim's baby, the other a man who was with them. The man and the baby are unharmed.
Politicians have expressed their outrage over what has happened. Prime Minister Stefan Löfven calls it "an unbelievable cruel act" and Justice Minister Morgan Johansson called the perpetrators "cowardly and dispicable savages".