THE body of a five-month-old baby girl left alone in the family car was first discovered by her older sister.

St Thomas More's Catholic Primary School teachers rushed to the car parked near the school after hearing the young girl's screams at 3.30pm on Thursday, sources told The Chronicle yesterday.

They thought the girl, in year three, had slammed her fingers in the car door. However, the teachers were confronted with the sight of the dead baby in its capsule.

One of the teachers began resuscitation on the baby, but could not revive her.

At a press conference yesterday, police refused to rule out the possibility of charging the baby's mother over the death.

Detective Senior Sergeant Lew Strohfeldt, of the Child Protection Investigation Unit, said "we will get to the bottom of this" and confirmed police had spoken to the dead infant's mother late on Thursday night.

"We have not ruled anything out and anything in," Snr Sgt Strohfeldt said when questioned by journalists over the mother's state of mind after the baby's birth.

In the first official police statement to the public since the discovery of the baby's body on Thursday, Snr Sgt Strohfeldt conceded police had very few details in relation to the circumstances leading to the discovery of the child in the rear of a Toyota parked in front of the school in Ramsay Street.

"At the present, we don't have a lot of information and we are currently interviewing witnesses for their statements," Snr Sgt Strohfeldt said.

He deflected a barrage of questions relating to reports the baby had been locked inside the vehicle for a number of hours, only to say that investigations were continuing.

Snr Sgt Strohfeldt said the mother was with the baby when police arrived.

"As you can imagine, she was very distraught."

He said the family was helping police with their inquiries.

"The full circumstances we really can't say prior to the post-mortem results from the autopsy," he said. It could be some days before results became available to police.

Police had hoped a post-mortem examination would be conducted yesterday, but that has now been delayed to today.

He said the investigation had proved "very difficult and stressful" for officers and emergency services involved in the tragic turn of events Thursday afternoon.

"It's a tragedy.......we'll get to the bottom of it."

Any witnesses at the scene are urged to contact Toowoomba Police on 4631 6333.

Director of Catholic Education for the Diocese of Toowoomba John Borserio said it had been a difficult day for everyone.