Queensland girl's appeal over mum's murder

A Queensland teenager who witnessed the double murder of her mother and uncle as a four-year-old has made a heart-wrenching appeal for public help to solve the cold case.

Detectives have reopened an investigation into the murders of siblings April and Ian Bailey who were killed before their Deception Bay home, north of Brisbane, was destroyed by fire in May 2004.

April's now 16-year-old daughter, Violet Bailey, said the killers have been allowed to escape justice while her family suffers.

An emotional Violet lamented missing out on "11 special years", and more to come.

"Eleven years ago I was a witness to my own mother and uncle's murder(s)," she said at Brisbane's police headquarters on Thursday.

"I would be ever so grateful to know that the people who killed my mother and uncle have been put into prison.

"All because someone thought they had every right to kill them I have missed out - I have missed out on 11 special years and I'm going to miss out on even more."

Violet was discovered uninjured at the murder scene by police, who believe recent advances in technology and forensic science could finally lead them to the killers.

A military knife and matching scabbard found at the house are being examined again while voice recognition systems are helping officers to decipher three triple-zero calls, where an argument and screaming can be heard.

Forensic investigations have already determined that the pair was killed before the fire was lit.

Detective Inspector Damien Hansen said police have received around six phone calls from the public with possible information about the murders since relaunching the investigation this week.

There is a $250,000 reward for information leading to the apprehension and conviction of those responsible for the murders and arson.

Police said indemnity from prosecution would be recommended for any accomplice, not believed to have been the offender, who provided information.