Convicted axe murderer Henri van Breda, 23, faces his whole life in jail "based only on circumstantial evidence", the Western Cape High Court heard on Tuesday.
"We are saying that a court of appeal may come to different conclusions on the facts," said his lawyer Pieter Botha.
The defence submitted that there was a realistic possibility, and not "merely an unlikely possibility" as found by the trial court, that unknown intruders could have gained access to De Zalze Estate that fateful night.
Botha was presenting argument before Judge Siraj Desai, in his application for leave to appeal Van Breda's conviction and sentence.
In June, Desai handed him three life sentences for the murder of three of his family members, 15 years for the attempted murder of his sister and one year for obstructing the course of justice.
Botha said on Tuesday that even if an appeal court upheld the conviction, there was a reasonable prospect that the State had failed to prove planning or premeditation.
"The mandatory life sentences then fall away and the court can consider sentence afresh."
Van Breda, who is serving his time in Drakenstein Prison in Paarl, was not present in court on Tuesday.
His girlfriend Danielle Janse van Rensburg sat at the back of the courtroom, listening to the arguments.
Botha said a court of appeal may attach more weight to, among others, the concessions made by State witnesses during cross-examination.
'Classic self-inflicted injuries'
Desai believed that Botha had not adequately addressed the "key pillar" of self-inflicted injuries in his application.
"The injuries in this case are classic self-inflicted injuries," the judge noted.
Botha's argument was that the court had erred in finding that the State had proved beyond reasonable doubt that his injuries were self-inflicted; and by rejecting Van Breda's version as to how the superficial cuts to his arm and chest were inflicted.
He also believed the court had attached too little weight to the evidence of two experts that the stab wound to the left side of his client's abdomen was probably 50mm, and not 10mm, deep.
Botha said it was crucial that the Supreme Court of Appeal was given an opportunity to deal with the matter, because of the complex evidence.
"I know of no other matter where so much DNA evidence, blood stain evidence and complex medical evidence was led, all circumstantial evidence which then requires a court to make a factual finding."
He argued that the State never shed light on the motive, especially given that the Van Bredas were a "happy family".Desai said the same could be asked about what the motive of an unknown intruder would have been.
Desai said that he had asked the defence during the trial for reasons to impose a lesser jail term.
"A life sentence, especially three times over, is a very severe sentence and your client is a very young man. I asked you several times to advance any reason in mitigation, I was asking you to give me a peg on which to hang my coat. You gave me no peg."
'You could ignore the DNA altogether'
Desai said the sentence would have been different if the defence had shown him that the crimes committed were the result of a "broken mind", or of a disturbed individual.
Botha said he could only work with the instructions he received, and his client maintained his innocence.
Prosecutor Susan Galloway said the court had correctly found there was premeditation.
She pointed out that, while the family was sleeping upstairs, Van Breda would have had to walk downstairs to the scullery to fetch the murder weapon, and then go upstairs.
There was also direct intent to kill because the axe was aimed at the head.
"Even if that evidence is not enough for premeditation, the facts and circumstances are enough that this would always have been a matter where the most severe sentence was applicable."
She accused Botha of nit-picking circumstantial evidence.
"He is again taking apart the circumstantial evidence and then missing the wood for the trees."
She said the court correctly found that not much weight needed to be afforded to the DNA.
"You could ignore the DNA altogether and come to the same conclusion," commented Desai.
He postponed the matter until Monday for judgment.