The validity of Henri van Breda's claim that he threw an axe at his attacker came under the spotlight in the Western Cape High Court.
He stands accused of killing his parents and brother in January 2015.
He has also been charged with the attempted murder of his sister.
The State's blood spatter expert Marius Joubert spent the week on the stand.
Under cross-examination, he suggested that based on physical characteristics, Van Breda's claim that he threw an axe at a masked attacker is untrue.
Joubert said that markings on the wall meant Van Breda would have been close to his alleged attacker, which would have made it simpler and more logical to strike him.
But the defence stuck to the story and said that there were too many variables to determine exactly what happened.
At that point, Joubert left the stand to physically demonstrate his theory.
The defence said the move created a false impression, but Judge Siraj Desai responded that he gets to make such a call.