Turku - Finnish police arrested five people in a Turku apartment overnight in their investigation into a stabbing rampage that left two people dead, they said Saturday.Police shot and wounded a knife-wielding suspect on Friday, arresting him minutes after an afternoon stabbing spree at a Turku market square. Police on Saturday raised the number of injured in the attack from six to eight."There was a raid and we have now six suspects in custody, the main suspect and five others," detective superintendent Markus Laine of the National Bureau of investigation told AFP."We are investigating the role of these five other people but we are not sure yet if they had anything to do with (the attack)... We will interrogate them, after that we can tell you more. But they had been in contact with the main suspect," Laine said.Police have not confirmed the identity of the suspect, but Laine said investigators were "pretty sure" they knew who he was.Police have so far only described him as "a young man of foreign origin", providing no other details except to say they were collaborating with the Finnish Immigration Service. The suspect is being treated in hospital in intensive care for a gunshot wound to the thigh.The motive for the attack was not yet known, and police have refused to confirm if it was terror-related."We haven't yet interrogated the main suspect because of his medical condition," Laine said.Media reports in Finland said police believed the suspect had picked his victims at random, but Laine could not confirm that.Police have said it was likely the suspect acted alone, but added they were looking for "other possible perpetrators."Central Turku was swiftly cordoned off after the attack, which occurred just after 4:00 pm (1300 GMT), although the area was reopened several hours later. Finland also raised its emergency readiness across the country after the stabbing, increasing security at airports and train stations and putting more officers on the streets.In June, Finland's intelligence and security agency Supo raised the country's terror threat level by a notch, from "low" to "elevated", the second notch on a four-tier scale.It said at the time it saw an increased risk of an attack committed by the the so-called Islamic State (IS) group.