From the information police have gathered since the blast they had enough to decide to question the teenager further.
The police does not want to divulge anything about his identity but say he is between 15 and 18 years old and previously known to them.
The object behind the explosion at Solbacken preschool was a powerful home-made firecracker, reported the police on Friday.
A four year-old girl injured her hands in the blast, and was taken to the hospital, where she was operated upon for several hours. The girl was still in hospital on Friday, but under the circumstances felt reasonably well.
According to police reports, it is believed that she will make a complete recovery.
“The girl found the cracker inside the preschool’s area. It exploded in her hand,” said the Stockholm police force’s Lennart Löfgren to newspaper Dagens Nyheter at the time.
The firecracker was lodged in the gutter of a shed in the preschool’s yard. When the girl pulled on the cracker, she heard a hissing noise before it exploded.
At first it was suspected that the incident was connected to two men having been apprehended by police on Wednesday evening, after being observed driving around the area throwing firecrackers into public places.
They were stopped by police a few kilometers from the preschool on the suspicion of devastation endangering the public.
But during the weekend police announced that they ere following up different leads.
When police searched the teenager’s house materials were found that indicate a connection to the pre-school explosion.
According to the police, bomb technicians were sent to the house to make sure that the materials found there are not explosive.
“We still don’t know exactly what the objects are,” said Erik Olsson to news agency TT on Monday.
The technicians didn’t find anything that could explode on the premises but they did find materials that could be used to make explosive charges, said the police on Monday afternoon.