DANIEL Morcombe's father has told his son's killer he picked the wrong family during a raw victim impact statement read out during Brett Peter Cowan's sentencing.

Bruce Morcombe told the Brisbane Supreme Court Cowan's actions had ripped his family apart and he was haunted by thoughts of the "unspeakable" things he had done.

He said Cowan had robbed Daniel, a child who would never hurt a fly, of 70 years of life.

"You made one monumental mistake that day," he told Cowan.

"You picked on the wrong family. Our collective determination to find Daniel and expose a child killer was always going to win."

Crown prosecutor Michael Byrne read out Denise Morcombe's victim impact statement.

She wrote about the love for her son Daniel, an innocent boy who loved animals and wouldn't have hurt a soul.

Ms Morcombe still had nightmares and was haunted by images of her son lying in "dark eerie bushland being destroyed by wild animals".

"I made a vow to Daniel I would find out where he is and justice will be done," she said in her victim impact statement.

"I have lived and breathed each day to find the answers."

She said Cowan was a "sexual freak" who had no respect for human life.

"This day hasn't brought closure, but the streets are safer without you walking them and looking for your next target to destroy."

He had "numerous and on occasions highly relevant" prior convictions, including two for raping boys aged six and seven.

Cowan was a dangerous opportunistic offender who'd shown no real remorse and had poor prospects of rehabilitation, the prosecutor said.

"Every right-minded member of the community abhors what occurred and what has been displayed in this court in great detail," he said.

Cowan's defence barrister Angus Edwards argued for leniency, saying his client didn't intentionally kill Daniel.

Justice Roslyn Atkinson paid tribute to the Morcombe family.

"There's nothing I can say to assuage the hurt and pain you've felt ... but your strength and the way in which you have conducted yourself has really been one of the main factors that brought us to this outcome today," she said.

The judge also recognised the "stunning" work by covert police officers to arrest Cowan, as well as the State Emergency Service volunteers who helped recover Daniel's remains.

Justice Atkinson said she wanted a some time to consider her sentence and adjourned the court.

Outside court, Daniel's parents Bruce and Denise thanked those involved in the delivery of justice.

"We have to thank certainly all the covert police officers, the SES searches, the scientific experts that all contributed to making sure a sex offender, a murderous sex offender, was caught and exposed for his actions," Mr Morcombe said.

Child protection advocate Bravehearts founder Hetty Johnstone commended the Morcombes for their resilience and keeping the issue on the front page.

"It has given us, others and the Morcombe Foundation a platform to get on there and talk about the sexual assault of children across the board," she told media outside court.

She called for stronger legislation to detain dangerous repeat sex offenders.

"Sadly, it is a classic case," she said.

"Here we have an example of when the system doesn't detain dangerous repeat sex offenders.

"Daniel didn't have to die, he should be here today if the system got it right."