Swedish authorities on Saturday released the driver of a double-decker city bus who had been detained a day earlier after the vehicle slammed into a bus stop in Stockholm, killing three people.

The public prosecutor's office said it ordered the release after the driver was questioned, and an investigation into the incident in the Swedish capital’s Östermalm district continues.

Three people were initially injured in the crash Friday afternoon. Regional authorities said Saturday that one person with serious but “not-life threatening” injuries, and another person with moderate injuries, were still hospitalized.

Police initially said they were treating the crash as “involuntary manslaughter." It wasn’t immediately clear what the cause was.

Swedish police said earlier Saturday — while the driver was still in custody and being treated in a hospital — that the criminal charges issued a day earlier remained unchanged.

The prosecutor’s office did not immediately respond to an email from The Associated Press asking whether it remained a case of suspected involuntary manslaughter.

Emergency services said the vehicle — a regular city bus — was not in service and no passengers were on board at the time, Swedish news agency TT reported.