Prosecutor Peter Larsson was told the news by investigators on Thursday morning.
“The information I have received is that it contains no explosives,” he told news agency TT.
Larsson would not reveal what was in the bag, saying that information was confidential.
“But it was a dummy,” he said.
The bag is being examined by specially-trained technicians in Stockholm. Larsson said he did not know when the investigation would be completed.
“We’re now looking for traces of the robbers in the bag – fingerprints or DNA.”
He denied that the examination of the bag had taken a long time.
“You have to be very careful when looking at a thing like this, to make sure that it doesn’t detonate.”
“The examination must also be carried out carefully so that no clues are destroyed.”
Police are continuing their investigation. A 37-year old man is being held suspected of robbery. A 39-year old man was arrested at the same time as him. He is suspected of aiding another robbery.