Police say it could be months before the cause of Friday’s fatal Ottawa bus crash is known.

Investigating officers have completed the on-scene investigation and removed the double decker bus involved in the smash at the city’s busy Westboro Station, which claimed the lives of three people and injured 23 more.

Ottawa police have released from custody the driver who was behind the wheel of the bus, which was almost at its 90 passenger capacity.

The driver was taken to the police station for an interview and released Saturday without conditions, Ottawa Police Chief Charles Bordeleau said.

“There has to be some sort of reasonable probable grounds to make an arrest,” CTV public safety analyst Chris Lewis told CTV News Channel.

“The shock of the situation after may have caused that driver to appear to be different than she normally would be.”

Lewis, a former Ontario Provincial Police commissioner, said he would be surprised if the investigation takes months because he expects police to find that the crash had a relatively simple and straightforward cause.

Officials initially reported that of the three people killed, two passengers were on the bus and a third person was on the platform. That, Ottawa Police chief Charles Bordeleau added, still needs to be confirmed.

“That was based on initial information,” Bordeleau said at a press conference on Saturday.

“Our investigators, part of their process is to determine exactly where those victims were, either on the bus or on that platform. So we have different pieces of information right now, so we’re going to correct that record.”

The names of the victims have not been released.

In a Saturday morning tweet, The Ottawa Hospital issued an update on the status of patients they received. One remains in critical condition while six others are still listed as serious and four have been upgraded to stable.

According to Miles Cassidy, the chief of Ottawa’s paramedic services, many suffered blunt trauma injuries.

At the press conference, Sgt. Cameron Graham said it will be “a long, detailed and complex investigation.”

“We are reviewing all aspects of the collision, including the vehicle, the roadway, weather and the driver’s actions,” he explained.

“Our job is to determine what caused the collision so we can learn from it and prevent such tragedies from occurring again. We will also be examining the factors in relation to any offences that occurred during this collision.”