The man who murdered his teenage son and his son’s girlfriend at Mount McIntyre a year ago has lost his appeal to have his 34-year non-parole prison sentence reduced.

Pawel Klosowski shot his 19-year-old son Lukasz and his son’s 19-year-old girlfriend Chelsea Ireland at his farmhouse on August 22, 2020.

His lawyer had argued that the sentence was excessive and failed to take into account his remorse.

These submissions were rejected by counsel for the Crown when the appeal hearing took place in the Supreme Court of Criminal Appeal in Adelaide earlier this month.

The three sitting judges handed down their unanimous decision to reject the appeal on Thursday and published their reasons for doing so.

The judgement described Mr Klosowski’s crime as so shocking and senseless that it transcended any ordinary understanding of human behaviour.

“The appellant’s offending involved a sustained episode of shockingly brutal, yet deliberately and purposefully executed, violence.

“Not only was this a double murder, but it involved an extraordinary response to what many would consider a banal domestic disagreement.

“The appellant’s offending, affected by alcohol, can be seen to be characterised by determination, brutality and purpose.

“As shocking and disturbing as the murder of Lukasz was, the pursuit and killing of Chelsea was simply senseless.”