The truth is that when the bank robber gave up, all the hostages—the real estate agent and all the prospective buyers—were released at the same time. One police officer was standing guard in the stairwell outside the apartment when they emerged. They closed the door behind themselves, the latch clicked, and then they walked calmly down the stairs, out into the street, got into the waiting police cars, and were driven away. The policeman in the stairwell waited for his colleagues to come up the stairs. A negotiator phoned the bank robber. Shortly after that the police stormed the apartment, only to discover that it was empty. The door to the balcony was locked, all the windows were closed, and there were no other exits.
You didn’t have to be from Stockholm to realize pretty quickly that one of the hostages must have helped the bank robber to escape. Unless the bank robber hadn’t escaped at all.