Daniel Morcombe’s killer has launched an appeal against his conviction on the grounds the jury should never had heard his confession to undercover police.

Brett Peter Cowan was sentenced to life with a non-parole period of 20 years last month after a jury found him guilty of abducting and murdering the 13-year-old Sunshine Coast school boy.

His lawyers filed a notice of appeal on Wednesday, saying the trial judge erred in not excluding Cowan’s alleged admissions of guilt to police.

They are also arguing there was a miscarriage of justice because several key witnesses were not called to give evidence and prejudicial publicity seen by the jury was cause for a mistrial.

Cowan was arrested in August 2011 following an undercover police sting, and Daniel’s remains were discovered in bushland in the Sunshine Coast hinterland later the same month.

Daniel vanished while waiting for a bus at Woombye on the Sunshine Coast on December 7, 2003.

Last month, Queensland Attorney-General Jarrod Bleijie instructed crown prosecutions to appeal Cowan’s non-parole period, saying it was not long enough and “manifestly inadequate”.

A spokesman for Mr Bleijie refused to comment on Cowan’s notice to appeal because the matter was before the courts.