The investigation now shows that the live hand grenade, which the National Bomb Squad later detonated, lay on the site for many hours, which P4 Stockholm was the first to report.
There was a great danger to the public since it lay there for about eight hours before it was disarmed, says prosecutor Anna Stråth to Dagens Nyheter.
The incident is part of a blackmail plot against the former stock exchange CEO Joachim Kuylenstierna, and the trial begins on Wednesday. The explosion at an apartment building on Östermalm in Stockholm in November will also be addressed.
A man in his 20s and three boys will be brought to court.
Five people have previously been convicted for involvement in the blackmail plot against Kuylenstierna.
