The teenage boys have been arrested on suspicion of arson.
Three of the boys were taken in for interrogations around noon Friday, and the fourth suspect was taken in later the same day.
According to Ulf Einarsson, in charge of the arson case, tips and investigation ideas led them to the four suspects.
"We've received many tips, and their names occurred repeatedly among the names mentioned," he said to news agency TT.
Thursday night's blaze has left the Berga Centrum shopping centre largely in ruins. Although no people were injured in the fire, the shopping centre could not be saved, despite work to extinguish the fire that went on through the night.