Chilling new details emerge about the cover-up of Tiahleigh Palmer's murder.

A 2016 police statement, unearthed by ABC, has shed new light on the extensive family cover up that followed the murder of 12-year-old Tiahleigh Palmer.

The victim’s foster father Rick Thornburn was sentenced to life in prison this Friday after brutally killing Tiahleigh, putting her body in the boot of his blue Ford Falcon, and throwing her remains into the Gold Coast’s Pimpama River in October 2015.

But now a police statement submitted by Tiahleigh’s mother and Rick’s wife, Julene, states how she watched on as her husband shoved her foster daughter’s body in the boot of his car.

Though she didn’t have clear vision of what her husband was doing in the shed half an hour prior to that, she knew her foster daughter had been killed by Rick as he went to dispose of the body.

“Don’t ask any questions … try to be normal — the less you know, the better,” Rick allegedly told the entire family the night of Tiahleigh’s murder, Julene disclosed in her statement.

The statement also describes how Rick ordered his sons, Joshua and Trent, to go out and try to be seen by other people. When his teenage boys and wife returned the next day, he told them he had "taken care of it".

When asked what he meant, Rick reportedly told Julene, “Don’t ask any questions, you don’t need to know."

"I have taken care of it. We do things like we normally do."

Tiahleigh went to live with the Thornburns after being taken from her drug addicted mother and spending time in various foster care homes.

It was with this family that Tiahleigh was sexually abused by her 18-year-old foster brother, Trent.

In September of 2015, Trent told his cousin about his inappropriate and illegal relationship with Tiahleigh, who told Trent’s mother, Julene.

Days later, Tiahleigh was murdered to prevent the word spreading of Trent’s behaviour, and the family covered up the murder.

Julene will serve a maximum of 18 months in jail, and Rick will serve 20 years before being allowed to apply for parole on September 12, 2036.